why do whites and straights defend blacks and gays when they get hated on?

They are secure in their sexuality!

Because it's the right thing to do.

It's only fair to do

Because its the right thing to do. 

We are all people and should defend other people against prejudice. 

Racist white person will take the word of a white person more seriously than a black person and a homophobic person will take the word of a straight person more seriously.

Lastly, there is less risk for a straight white person to speak up. A racist homophobe is less likely to resort to violence if speaking to a straight white person. 

Because we don't do a good enough job to tell them that they should mind their own business. (Which is equally important, and any who don't wish them to so must by the powers of equality needed to let lgbt keep their rights be considered true supporters of homophobes rights to voice their homophobia)

Because they are fellow human beings who are getting hated on for extremely poor reasons, and it's the right thing to do to defend others who are getting attacked.  It's about equality in society, law, respect, and dignity  The real question is, why do you think they shouldn't?

Maybe because it’s the right thing to do. And that same jack hole who is doin the hating will hate on something the “white” or “straight” is legally doing while going about their own business too.

Hateful bigots don’t just stop with one act or one chosen group.

Why not?

What reason to you have to hate people over race or sexual orientation, other than being a racist or a homophobe, or basically a facist?