Even if you don't want to say "No" on everything, there's a time and place to say "Yes". As in, sometimes, the answer is "No, but if you want to register a preference for certain options in the next campaign, it is duly noted."
Now, with Tielfings, I dislike them so intensely as a character conceit that my answer on that is, "If you want to run a game with them in it, I might play, but don't count on it." Some things just get a hard veto because the GM is the one doing most of the work. Lots of other stuff, I don't necessarily have anything for or against it, but I do want a campaign developed with some coherence and focus. That is, not only not a kitchen sink approach, but even in a setting where the pool of available races is wider, I want a given campaign to focus on a smaller set. (For this reason, in D&D we sometimes have a limited race choice at 1st level, that will explicitly open up a little for replacement characters at higher levels.) Logically, that means there are lots of "playable" races running around in the setting that you may encounter--but you still can't play them! Not yet, anyway.
Fortunately, I only play with people mature enough to understand that not getting what you want right now is different than not ever getting what you want.