Some people believe that they will never require the service of a criminal lawyer; they obey the law and just go about life. Every day when we wake up we do not know what the day will bring. It could pass quite uneventfully, or something terrible could happen which results in being detained by the police and/or charged with a criminal offence.
Some examples might make this a bit clearer:
Example 1
It’s been a long at work and you get into your car to drive home. You didn’t sleep too well the night before; the baby kept you awake most of the night. As a result, you’re rather tired by the end of the day. You’re driving along the road and you momentarily lose your concentration and before you know it you’ve been involved in a collision. It’s fine; the insurance will sort it out. However, a passenger in the car you hit dies as a result of the accident. Suddenly, you find yourself in the middle of a police investigation. You’re later detained by the police and suddenly find yourself needing the services of a criminal defence lawyer. You get one and they steer you through the interview, but the decision is to charge you with causing death by careless driving. It’s serious; you’re facing a prison sentence. You‘re going to plead guilty, but you want the shortest sentence possible so you instruct a defence lawyer to represent you. You’re not particularly well off, but suddenly you’re facing a three figure bill as a “contribution” towards your legal aid costs. You’ve always tried to live a good life; you don’t steal things and such like. However, you’re in the middle of the criminal justice system facing a prison sentence of up to 14 years.
Example 2
A lot of people like to go out and have a good time; often drinking far too much and becoming intoxicated with alcohol. Someone rubs you up the wrong way and you give him a bit of a punch and they fall over hitting his head off a nearby table. Unknown to you at the time you punched them the victim has a weak skull and dies as a result of your actions. Thinking everything would be ok, but without checking, you walked away; you didn’t summon any help. A few days later there is a knock at the door and a couple of police officers are on your doorstep. They inform you of what had happened and detain you on suspicion of murder. A little extreme you might say, but entirely possible. You’re suddenly, out of a drunken shove, facing the most serious charge in our criminal law and the possibility of serving a life sentence. Suddenly, you need the services of a criminal defence lawyer. In the end you get charged with Culpable Homicide, but that’s still a serious offence potentially carrying some serious time in prison (up to and including life imprisonment). You’re now also facing a significant contribution towards your legal aid.
Example 3
A third and final example of how easily it is from your life to turn into a living nightmare where you, an otherwise innocent individual, find yourself caught up in the criminal justice system as the accused. Some new neighbours move in next door. You don’t get on with them and a dispute begins between you and them. Things don’t start off too bad at first, but the quickly escalate. One day you’ve had a bit too much to drink and you start having an argument in the street with said neighbour. Another neighbour calls the police who turn up and you end up back at the police station accused of committing a breach of the peace. You think you’re fine and don’t get a lawyer at the police station. Things don’t go quite how you expected them to and you’re charged with committing a breach of the peace. You now consider that you need a lawyer, but when you find out that you’re going to have to make a contribution of your costs you decide you can’t afford to instruct a lawyer and you go it alone trying to represent yourself. Any decent solicitor will tell you this is a bad idea; not because they lose out on fees, but because it usually ends up badly for the accused. A non-legally trained individual trying to defend themselves against the might of the state which has money and qualified lawyers at its disposal is a significant imbalance in power and really isn’t going to end well. Yes, the court will try and assist an unrepresented accused, but there is a limit to what the Court can do. In this case it goes badly for you and you’re convicted of a breach of the peace. You now have a criminal record; a criminal record that might have been avoided had you been professional represented by a defence solicitor. A solicitor might not have got you acquitted, but they could have worked to reduce the level of fine or community service you get.
All of the above three examples sounds farfetched and extreme; “it’ll never happen to me” you might say. However, they are examples of what could happen to any one of us on any given day (and there are many, many more). All of them resulting in an otherwise law abiding citizen being caught up in the criminal justice system and needing the professional services of a criminal defence lawyer. One day it really might be you and you are in need of criminal legal aid. However, the legal aid has dwindled; it’s almost impossible to get because of government reform and requires you to put up considerable amounts of money that you simply might not have. If you’ve never thought about it before I challenge you to think of all the things you do in a day which could lead to you needing the services of a criminal lawyer; I’m sure if you really think about it you will come up with many.
This is why criminal legal aid matters to everyone (it’s also why the right to a fair trial matters to everyone).
prout de jure 
Don’t forget in example 2, it might be the other person who swings at you first; you punch the back, they fall over and things happen as described. Even though you may have a perfectly good legal defence of “self defence”, that does not mean you will not get charged with culpable homicide or murder and have to go to court to prove what actually happened.
Without professional assistance of a lawyer to examine the prosecution evidence and assemble your evidence of what actually happened, it is entirely possible that the fact that the deceased “victim” was in fact the perpertator may never come out and you end up convicted.
Example 4. You are separated from the mother of your children. It hasn’t been pleasant. She decided that you weren’t going to see your kids any more so you had to go to court where you had to sit and listen to a catalogue of fictitious allegations against you. It’s never easy to prove your innocence but the sheriff found the allegations to be groundless and made on order for the kids to stay with you alternate weekends as well as picking them up from the school one evening a week.
You turn up to collect them from school on Friday afternoon for their weekend with you to discover she has already collected them. You go to th house and ring the bell. You ex tells you, “You’re no f******g gettin’ them and slams the door. You ring the bell again and are still on the doorstep when the police arrive. She has dialled 999. Because you are on the doorstep you are lifted and spend the weekend in the cells. To your complete amazement you are charged with domestic abuse aggravated threatenening behaviour. It is a set up and entirely untrue. You are tempted to plead guilty to get it over with but realise as soon as you do she will be back in court to cut or remove your contact with your children. This is when you need a criminal defence lawyer to bat for you. The stakes are far higher than the police can be bothered with.