Online dating stands on its own in that it is a very front loaded experience in terms of getting to know another human - the judgement begins much before any interaction occurs. That is not the case in any sort of similar degree when you meet someone say at work, or in a sports club, or even in an online game or internet forum.

And as you point out, that makes the notion of a dealbreaker a fairly nuanced one - e.g. I might tell myself that I would never date someone who doesn't want kids because I do want kids, so why would I waste my time? On a website that shows these preferences, I will likely not engage with profiles who mention that they don't want kids, and ignore their messages.

But of course when the new guy shows up at work and he turns out to be really cute and interesting, I may be interested in him/we may start a romantic relationship before these preferences become apparent.

Which can then go in any number of directions - the relationship might fizzle out really fast. Or it may engender personal change for the partners. Or it might lead to many decades of bitter resentment. Who knows! This could make the rational argument that one should accept to chat with anyone on a dating profile regardless of their displayed preferences, but of course that's not how humans tend to reason.