Strongly disagree with your position. You state it's unsafe then when he wants to get something done that is safety related like brakes, you refuse. Ironic to say the least.
With all due respect, you do not seem fit to assess safety of a vehicle if you don't even see how important good brakes are. It is a bit dubious that when you attempt to list the safety issues, it is merely power steering squealing and a wheel wobbling. If there had been anything worse, you would have mentioned it for sure. Either of these things are well within the capabilities of a shadetree mechanic in one afternoon.
I'm not suggesting that a bent rim shouldn't be fixed, but obviously this guy is strapped for cash and at least trying to get something done when you were contacted about the brakes.
Further you have supplied no supporting argument about how his prior wreck was due to poor maintenance, or are you just assuming it? People get in accidents all the time and besides underinflated or worn out tires, poor maintenance is not the usual cause.
Some people simply aren't car people and will do the minimum necessary to keep it running. That he has an old car is evidence in itself that he can't be TOO accident prone or he wouldn't have had the vehicle long enough for you to notice things needing done a year ago, rather it would have been wrecked and put in a junkyard already.
The fact is, you looked at it a year ago and he drove it for a year without the sky falling, so your assessment of the grave danger was apparently not quite accurate.
Y weren't teaching him a lesson or anything like that. You just caused him to drive on old brakes till he finds someone else to do it, the same as your passing on doing other repairs he needed (quote " repairs needed were so extensive that I told him it was above and beyond what I could do for him", but then all you could come up with was squeaking steering and a wobbling wheel).
I can completely understand if you are not willing to donate multiple days of your time to do the repairs, but that is where the judgement should end. Perhaps you should work out a modest payment to make it more worthy of your time, and if nothing else, buy some tools that speed up your productivity so you can get more work done without it seeming too daunting.
On the other hand, certainly you have no obligation to maintain his vehicle and it is his burden to operate it safely on public roads. I just think you overstepped your place in this, a couple different ways as mentioned above, and that your expressed intention and the end result are at odds with each other.
At the same time, I see and agree with your point of view that you should only be helping when reasonable, not becoming the primary responsible party for maintaining HIS vehicle, that he probably drives vehicles that shouldn't be on public roads, but the thing is, he apparently is doing so, and isn't going to stop (pun intended)... brakes can at least improve the safety of others.