Flagging is for when things are against site guidelines. Downvotes just mean disagreement; it's been that way since forever, and pg has stated that downvotes-for-disagreeing is fine on HN. They're just imaginary internet points anyway.

The stupid thing is that it just takes one person disagreeing in order to grey out your text - that's an HN fault, not a human fault.

> shouldn't people be offering me counter-arguments instead of downvoting?

Probably, but there's a lot of things people should be doing which they don't do.