If everyone was strictly fundie, how would the human race survive?
Answer: It wouldn't. It's a fact of life that, because of the thousands of denominations that exist, there'll always be conflicts - from doctrinal argumental to outright internecine war. As a result, said fundie world would be reduced to a situation a la "Lord of the Flies", with people killing each other over 'who was fundier than thou'.
...but such a scenario will never come to pass. For one thing, the US Constitution - and the armed forces sworn to defend such - from enemies both foreign and domestic - will ensure the Dominionists' dream will stay exactly that: a dream.
Then there's the little matter of the rest of the world, such as we in Europe who aren't as obsessd about religion as you lot are over the 'pond'. Remember: we have armed forces too (as well as nukes; one word: France). And don't forget the (at best) irreligious Peoples Republic of China. PROTIP: they have nukes too.
...meanwhile, back on Planet Reality, gay men exist. They have existed since time immemorial. And they'll continue to exist, making the world just that little more fabulous. And heterosexual couples still have children.
I love the smell of destroyed hypothetical questions in the morning. Smells like... victory.
@Mike
"Two words: artificial insemination."
callumevans324 had better not watch the anime series "Vandread", if he knows what's good for him:
http://en.wikipedia.org/wiki/Vandread
Specifically how in this future scenario, humanity had split up gender-wise, to form the parallel worlds of Taraak (male) and Mejerr (female) - and the methods used by both to reproduce.