[Note: I'm pretty sure none of my readers would mock a contestant, so please don't think I'm speaking to you personally, so much as the entire Internet. - Hillary]
1) It's not nice. (Didn't your parents teach you any better?)
2) It's not sporting. They can't answer back, after all. And leaving genetic advantages and presumed plastic surgeries aside, they've probably worked hard and strategically to succeed. Also, the whole, "Give me a quick, meaningful answer to a profound question, only be sure not to alienate any of our millions of viewers" situation is a trap. (How well would you do, especially on national television and while wearing a girdle and high heels?)
Besides, many contestants come from economically disadvantaged backgrounds. (This study--admittedly from 1998; couldn't find anything more recent--found that 21.5% come from families with incomes of less than $30,000, and nearly 74% come from families making less than $60,000.) Many contestants probably see pageants, rightly or wrongly, as one of their best paths to success. (It's no accident that pageants often dangle scholarships as a prize, although doing so also helps them pretend they are a wholesome activity, instead of the sexist, exploitative relics they are.)
3) It's not helpful.
Some mockers justify their behavior by saying it teaches the contestant a lesson about speaking sloppily in public. (I'm not making that up! See, for instance, the comments on this article.) That's self-serving garbage, frankly. For one thing, the contestants obviously aren't even aware of your so-called "lesson." For another, they don't need it: they have teams of experts to coach them. (I wouldn't be surprised if some are coached to not sound "too smart.")
For another, learning mixed with nastiness doesn't work. (Would it work for you?)
Finally, it's pretty obvious you don't care at all about helping so much as participating in the fun of an Internet pile-on. (See also: mean.) And as to delivering your mean comments about someone's public speaking from under a cloak of Internet anonymity...I'll just let that speak for itself.
4) It's also not helping you.
People who harshly judge others are also liable to harshly judge themselves, a form of perfectionism that can fuel procrastination and blocks. In fact, there's a good chance that it's the suffering that arises from your perpetually judging yourself that is causing you to seek relief by reveling in someone else's weaknesses.
Mock the contests, if you want: in fact, they should all be mocked till they die. And it's okay to mock Donald Trump, owner of the Miss Universe and Miss USA pageants, who is also generally a jerk. Mocking is actually a great way to take power away from those who use it for ill.
But don't seek to demonstrate your own aversion to superficiality and ignorance by superficially and ignorantly mocking beauty pageant contestants.