Because it takes from a few people and gives to many. More people would vote for it than not.

Ah, Robin Hood democracy. Of course villagers would vote to take away from the king and give to themselves. It all depends on the perspective - if a regular Joe Smith realized that his child will not be able to keep his house because they would never afford to pay 85% of its value in tax, they might not vote for such a law.

Mere details. Certainly one could devise a tax code complex enough that Joe Smith couldn't hope to judge its effect on him.