Never having been on OKCupid, I don't know if they have a standard questionaire as well as a space to write something original. I once used another dating site where this question was part of that [standard questionaire* (with multiple choice answers)]. You could opt not to answer, or tick as many of the answers as you want: anything from "pen pals" and "friends" through "flirting" and "just sex" to "LTR" and "marriage". One of the options was "Let's see how it goes". This seems to be your choice, but you should specify some parametres, eg. "No emotionless sex", "Let's take it slowly"...
Since you write "I get asked a lot what I am looking for", I assume that you're asked this by guys [and gals?] who have seen your profile and got in touch.
Once you've binned the wackos and repulsive types (though people who ask this question aren't very likely to be either), why don't you send them that message in the quote above? (n.b. I've corrected "before hand" to "beforehand".) Concise, open to further interchange, honest. You could add details of what you don't want.
Any help?
* Used to computer-evaluate compatability. You could also rate the importance of your choices from "not important" and "mild preference" to "essential", so that, e.g., you could set "wants to have children" as "essential", which would give you a 0% compatability rating with anyone who had ticked "no", "maybe", or "wait and see".
More pertinent to your case: You could tick every answer but "just sex" in the 1st Q I mentioned, tick "essential"... and that would weed out anybody who included that as one of their options.