Why so much hostility to the idea of world government?

I've noticed that there is an enormous hostility on this board to the ideas of global governance or world government which would be the most complete form of global governance. Why does everyone automatically assume that this would be a bad thing?

It could be a very bad thing, of course, if the government was a bad government. But couldn't it be a desirable thing if the government was a reasonably good one? So many problems in today's world are not being solved because nobody has the authority to solve them; problems such as human trafficking, the international drug trade, and human rights violations by national governments. A world federal government should, in these cases, be able to step in and resolve such problems. The present UN may be a step in the right direction but it is very inefficient.

I would be willing to accept a level of government above the national one of my country. Would you?