Should your friend break up with her boyfriend if he wants kids and she doesn't want children?

It’s absolutely a deal breaker. It’s unfair to expect one who desires children to give that up for the sake of the partner. Generally people who think they can change their potential spouse regarding any topic is irrational and will lead nowhere 

Break up....He wants kids and will take it out on her forever, or he will go and have a child with another.

YOU should butt out of your friend's business and take care of your own life.

She's probably a 5 or a 4 but he still dates her.

You should break up with, because eventually it WILL become a problem. Save both of you a lot of pain and heartache and break up now. Let him find a woman who wants children, and you go find someone who feels about it the same way you do.

Yes, if she wants a man who doesn't want kids she should find one and she also shouldn't lie to the man (that takes away his choices). 

There are plenty of men who don't want kids!

Yes, he should. That is a difference in life goals that is too fundamental to overlook. Trying to coerce someone into changing what they fundamentally want out of life isn't love and will only ever lead to resentment and hate that will utterly destroy the relationship, so better to end it now than waste years or a lifetime mired in unhappiness for one, the other, or both, because that's what we're talking about 100% and that is 100% for sure what's going to happen if anyone is stupid enough to go with that stupid "Or should she marry him hoping he won't pressure her to have a baby" plan.