The point is, if I say I want X, then you rightfully assume I do want X and not Y.

No. That's just what I pointed out to you. You assume that "I am looking for X" means "I do not want Y". That is an assumption you make, and you can't blame others when it turns out wrong.

I'm not saying that your assumption isn't correct much of the time. But what you are assuming isn't explicit in their statement, and there are situations in which your assumption is wrong. When those situations inevitable occur, you can't then whine that your assumptions were incorrect.

Yes, there are a lot of situations you can imagine where the sentence "I am looking for a relationship" means "I will not pump and dump you". But there also exist situations where it doesn't.