If you had the power to change one law, what would it be and why?

Many people use loopholes in the law to avoid paying taxes. By moving their funds offshore for instance or using accountants to hide their money, and filing tax returns with lots of expenses included so their tax charge is reduced. In this way poorer people on income tax, paying as they earn, can pay a higher proportion of their income in taxes than those who are richer than them.
Avoidance is legal, evasion is not. Quote:
Tax avoidance is the legitimate exploitation of tax loopholes to reduce the individual or business’ tax liability whereas tax evasion is the illegal evasion of taxes properly due.
So why do we allow this? Especially the most egregious examples of avoidance? Yes, there should be legitimate reasons to cover normal expenses, but surely we could cut down on loopholes. Maybe every country could have the same tax rates, so no one can get away with it. I understand some countries offer lower taxes to increase their income, but there might be other ways of doing this. I think it would be difficult but not impossible?
It can’t be right that about 80 men have more wealth when its added up than half the world’s population. In other words 80 people have about the same as 4,000,000,000 people! Once you look at it that way it’s not really fair is it?
