AFIK the reason for taxation is we all want to live in a safe and prosperous environment.
That in turn means we need protection from those who would steal our sheep and rape our wife (or steal the wife and rape the sheep, same principle). For outside of our nation (a somewhat arbitrary boundary, usually resulting from hundreds of yeas of bloodshed and the odd natural boundary) it means we need some armed services and intelligence agencies , and inside that boundary we need the police and legal system. All has to be paid for.
We also want things to be generally clean and safe, so we need things sanitation and refuse disposal, health care, some standards and enforcement of employment law, etc. For long term prosperity we also need education so those who are able can do well in employment, not just those lucky enough to be born to those who value and can afford to pay for it. Bitter experience has shown that most people are lazy and will try to avoid "public spirited" support, very much so if it costs them money, so we also have to find a way of making sure it is paid for. So we have taxation.
"why not negative income tax for individuals"
Is that not one key aspect of the welfare state? To provide support for those who cant otherwise afford food, shelter, etc? While it might be popular in certain political circles to class them as spongers and time-wasters, and I dare say there is a proportion who are like that, the reality is a lot of folk will find themselves out of work at some point in their lives for any one of a number of reasons. Without support they could well end up as 'unemployable tramps' and never get a 2nd chance. Even if you are totally self-interested you should still want some welfare state, as poor and hungry people may decide to take your property and maybe life as well since they have little to lose.
I am not saying current governments are optimum, but it is a hell of a lot better than the pre-taxation days.