Most Helpful Guy
I think it depends on the person.
For guys that also are absolutely certain they don't want kids, well then, I guess they don't have to worry that You want kids or would change your mind eventually about them or also try to change their minds about it. So that may be the quite opposite of a deal breaker and you might draw more attention from guys that are certain they absolutely do not ever want any children. Not too sure about the adopt thing well I guess that's slightly different. Best that both partners can compromise on this matter and come to a full agreement if they are absolutely sure that they both would rather adopt some kid (s) instead.
I just think that would make things much easier for both partners and relieves any additional discomfort and unease when it comes to that subject matter. Otherwise, it can not possibly ever work out, regardless.
If you are absolutely serious about it, then maybe it's best to go through some medical procedure called sterilization, such as 'Tubal Ligation' or 'Hysterectomy', and demand the same from a guy to prove they are serious (once your relationship eventually starts to get serious) and provide that they have proof that they had gone through a sterilization procedure such as Vasectomy.
Either way that will make it certain for the guy that don't want kids that you are absolutely for real, leaving absolutely no room for error or accidental pregnancy from either missing a dose of birth control pills or because of a faulty condom or something similar.