I've been here only a few days and even I know this 'answer' of yours is wrong.
The reason that I think most people hate on 24's is because most of them are Hunters, Paladins, and whatever other strong classes there are. Coincidence? Nope. Most people roll 24 to destroy the F2P 20's because they have a HUGE advantage over them.
We F2P players play F2P because of a few reasons (at least for me):
1. I don't want to give Blizzard my money to play at low level when I'm tired of their
low quality high level content (played high level since TBC but it's unappealing to me now)
2. Free-to-Play is a new unique style of PvP with heavy restrictions. It's a refreshing change compared to everything else that has been introduced in WoW for the past years.
In general it's a refreshing way to twink without handing money.