Personally the kids thing would be a deal breaker for me. I've always wanted kids and understand that some people can't have biological children, but there are other ways to have children (adoption). Having a few kids has always been one of the most important things to me, so I'd want to partner with someone who felt the same way. Having said that, I can understand why some people don't want kids...and believe they should partner with people who also don't want children.
My hubby and I discussed all the deal breakers before we got married...but now that we are married there is an understanding that if a deal breaker issue came up (for example, drugs, alcoholism or other illegal activites), we would try to work through it together if the person affected agreed to get help and tried to change...we wouldn't just walk away automatically. I've already been through this with my hubby in regards to verbal abuse (an issue I never foresaw being a problem prior to moving to the UK and realizing my hubby has extreme anxiety - which was fairly easily hidden from me prior to living together). After I realized it was a problem, I explained it was a deal breaker and he could either get help and change (I would help him as much as possible) or we could get divorced.
The way I look at is like this: if one person is going to regret a decision for the rest of their lives (which can lead to contempt and possibly cause you to resent - or hate - your SO for the rest of your life), that should be a deal breaker. Yes relationships require some sacrifices and that's one thing, but giving up a life-long dream to appease the other person (or to avoid an argument or to make the other person happy - or for any other reason) is something different altogether.