So...let me tell you what I think you're saying and you can tell me if I'm right:
You're saying that, "I don't like it." is inferior to almost any other answer one could give, but it's still acceptable.
Erm. Not exactly.
In most cases, "I don't like it." is inferior to almost any other answer one could give, but it's still acceptable. However, it is impossible from the outside to predict where the "not most cases" lie.
One of the first things a therapist will teach you (and EN World mods, for that matter) is to walk away when you're feeling heated, rather than saying something you might regret. If someone is annoying you by repeatedly questioning every setting decision, then, effectively, "I don't like it" is like walking away.
One of the first things that being a parent will teach you is that this is sometimes necessary. Because children can and will use "Why not?" as a sort of verbal weapon.
One of the things one learns as a GM is that some players will do the same thing.
As I noted upthread, by the time "because I don't like it" appears in the conversation, it is almost certain that either there is a bad (badgering) player involved or a bad GM. Someone who is actually curious about why you don't like something is far less likely to be annoying that someone who wants reasons to drive their own agenda.
Frankly, if the player was merely curious, I doubt this thread would exist. If the player is merely curious, and the GM is annoyed by that (respectfully addressed) curiosity, then perhaps being shown the door is actually a service to that player. Before he gets too involved with that GM.
There is also a time and place where "But why not?" is appropriate, and a time and a place where it is not. All things in their season.
If I'm understanding you correctly then I'd counter by saying the purpose of places like ENWorld (to my mind) are to let us exchange ideas that will make our games better. Therefore it is appropriate to respond to a thread such as this by askiing, "You could give that answer, but why would you since almost any other answer would be better?"
If you start with "You could give that answer", then the rest might actually help the poster, who has a question about player behaviour rather than his own.
I would also note that, to some degree, your question is answered in the OP. Being asked repeatedly to justify your design decisions/preferences can be annoying.
Methinks its the age-old trust issue all over again.
Do I, as gm, trust my players to respect my role and treat my creation as I intended it?
Do I, as player, trust my gm to have a clue what he´s intending with the rules and not just using his position to enforce his will on me.
Methinks you've nailed quite a bit of it here.
I would add, common courtesy need yet apply, and if the answer is No to these questions, either as GM or player.....
run! You can find a better game. Or better no game at all.
IMHO. YMMV.