I voted permissive.
My line in the sand is: Is the player being exploitative, abusive, or coercive?
Exploitative behavior is using the game or table rules in a manner that contradicts the spirit thereof or the tone and style of the game. Exploits
technically work, but do so only by perverting or defying the overall goal and ethos of play. Anyone actually trying to adhere to the spirit/tone/style of the game is pretty much perfectly shielded from being exploitative--and it's
really not hard to tell when a player is sincerely trying to do that in most cases.
Abusive behavior is when a player is being hostile or hurtful to other players (including me as GM--on both sides). I shouldn't have to explain why that's not acceptable in any circumstance.
Coercive behavior is manipulating other players into doing what you want, without their consent or even against their will, generally (though not exclusively) with the goal of being better or being the one "in control" etc.
As long as the player is genuinely enthusiastic about something, they will not exhibit any of the above characteristics, and thus I will do anything in my (considerable) GM power to pull it off. It may require some adaptation or alteration from the player's original vision, and they'll need to be comfortable with that. But as long as it isn't one of those three bad things, all they have to do is sell me on it--and I am quite easily sold on most things.
But these things are not given as specific examples of using it. "Restrictive" means that if it's not specifically mentioned in the rules, you can't do it. If you say "okay, make an athletics* check" you are being permissive, even if you set the DC to 35.
*Or other skill. for example, I would ask for a Religion check to make an improvised holy symbol.
Whereas for me, I would classify both of those behaviors--"no, you can't do it, it's not in the rules" and "sure, you can 'do' it, but it's DC 35"--as being restrictive. The latter is just making a pretense of being permissive by
pretending to allow things while actually banning them. I don't like either of these behaviors, but I have a special antipathy for the latter, as it is deeply disingenuous.