I've seen UN Sustainable Development Goals. They are all worthy of doing and lofty. Countries often impose those goals on the population by introducing regulation. Meanwhile Russia seems to be against all humanitarian goals... Why is it still allowed to be the part of UN? If a regular citizen did what Russia does, he would be in jail. Yet Russia is still allowed to take a seat with more civilized leaders. And no aggression is done against Russia.
The UN was created to give the winners of WWII a forum to debate their differences and to prevent future wars. The three main victors were the US, UK, and Soviet Union, with France and (then Nationalist) China in the next tier. Russia inherited the Soviet seat and the PRC inherited the ROC seat.
If UN membership was contingent on the human rights record, it would not allow opposing sides to talk about their differences.
Because you are misunderstanding the purpose of the UN.
The UN isn't some group that makes rules which all the countries have to follow.
The UN is just a place where countries talk with each other - and then behave how they wish.
It has no enforcement power whatsoever, although it's very common that many countries will agree that something (such as human rights) is a good idea, and enforce it amongst themselves, and this initiative may be officially part of the UN. Despite being part of the UN it has no power except for what the participating countries give it.
If you kick Russia out of the UN, you decrease, for example, Russia's ability to tell other countries "we will nuke you if you do this" or "we oppose democracy." You don't actually decrease its ability to nuke countries which do this, nor its ability to oppose democracy.