I'll say this upfront - I don't have my position on homosexuality straightened out. Or worked out to where I'm comfortable saying exactly how I feel (without sounding like a religious bigot).

Can people be born gay? Some seem to think so. Some would point to a time when they were very very young and could identify their first crush as a person of the same sex. Much like I (being straight) can say without a doubt, my first crush was a boy.

As for why would God let them be? Well, he lets robbers, rapists, murderers, theives, liars, backstabbers, abusers, you-name-it kinds of people survive, or be born into the world... Who knows why He hasn't pulled the plug yet?

The lifestyle can be said of most of us: sexually active outside of marriage, experimenting at a young age, drunkennes, drug use, etc etc.... So it's not just gay people who are engaging in "sinful" lifestyles.

And at the end of the day, we are all born with a sin nature. We each have our own cross to bear.

Its simple.  -They aren't born that way. 

Though people may be born with certain behaviorial or personality traits, I personally believe it is the environment the child is brought up in which determines the kind of adult they will become. 

And until the child is old enough to know how to reject evil (and is able to) they are extremely impressionable. 

And in this age kids, as well as adults, often don't know they need to reject those thoughts. 

Also, as I've said before, there are so many children growing up without healthy examples for gender role models.  Kids learn by example and by watching, and so many boys never learn how to be a healthy masculine, yet balanced and loving man, husband and father.