Why not set it up a la carte? See what public services people feel are worth paying their money for? It might actually get more rational public spending by pushing people to think about just where whatever public service they think would be cool and nifty to have will come from, especially since for things like 'community pool' you could have the trigger not be 'majority' but 'sufficient funding.'
Because people are idiots.
Likewise, if I don't pay for social security, and I don't have savings, that means I'm poor in old age. Which makes it more likely I'll go robbing stores for food or begging on the street. Is that a better outcome for society - to have homeless or higher petty crime just for people who fail to plan?
You do realize that I'm figuring that the odds of social security surviving long enough to pay me and most others of Gen Y & above a single penny is so low as to qualify as a sadistic joke, right? If a non-government organization tried running social security it'd be shut down because it's a Ponzi scheme--the original assumption was that the population would keep climbing and life expectancy would be stable, given that the odds of you living long enough to see your first social security check when it was set up started pretty bad and dropped towards laughable for the poor.
We're in full agreement that people are idiots, but I'd like to point out that not all cultures even organize emergency services and care of the elderly/disabled the same way--and some of them really are rather healthier in many ways because of the issues involved in making things Somebody Else's Problem.
And that's the real problem - that's why we collectively pay into emergency services - sure it'll be very unlikely to happen to *me*, but you know, I'd rather spend my days and later years in life not worrying about all the old seniors who decided to live it big when they made money and not save up who might come and rob me, or to just be able to go out and enjoy parks without tent cities of same.
Congrats, you just covered why emergency services definitely need paying for--though you still have the question of why exactly I should trust Social Security to stick around, since whatever I pay into it now is going right out the door now. It's not an investment scheme, it's not a lockbox, and if anybody but the government tried running it then it'd be very, very illegal.
Even today, a significant chunk of the population lives paycheck to paycheck - miss one and there's a good chance they'll be out on the street, likely raising the local crime rate all so they could feed their kid (and we all pay for it - increased prices, increased policing/jail/courts/etc). There's a good chunk of people not living
And yes, there's a good chunk of people not paying income taxes - but they're both rich AND poor. But they're paying taxes in other ways - state taxes, sales taxes, etc. They're not getting a free ride.
Which also suggests a way to cover the emergency services, because part of the entire issue here is that if you're living from paycheck to paycheck, then the more of that very same paycheck you can take home the better. You could probably get fewer people living from paycheck to paycheck that way, if nothing else.
As you said, people are idiots; why give them a blank check? Even threatening them with an a la carte system and making them argue for why any given part needs to be in place would help. (Especially since some of the differences between cultures which consider, say, care of the elderly the problem of their kin vs the problem of the government are interesting--particularly in the differences in what the outcomes tend to be when it is viewed as your problem to deal with as opposed to a nebulous governmental one.)
Really, I figure that people are such idiots that giving anybody the ability to forcibly collect funds to provide what they have decided with minimal consideration to be social goods is something to be very careful in doing--if they're not going to think ahead about themselves, which they've got good selfish motivations to do, why should I expect them to somehow become smarter when it's for a common good? (Hell, we're not even sure altruism exists for a reason: there's an ongoing argument that nope, it's basically just ego-wanking.)