Well, hold on a second.
There's "reasonable" as in, "it is reasonable physically - pockets can be picked". Then there's reasonable as in, "this is a reasonable plan that a sane person would consider a good idea". It is reasonable in the first sense, and not so much in the second sense.
Now, great adventures are often built on unreasonable plans, but you generally ought to have the agreement of others at the table before you impose the results upon them. It is all well and good to say that folks understand consequences - but a player need to know that his actions have consequences for the other players, as well as their characters. This is a cooperative game, and keeping that in mind is the kind of metagaming that isn't so bad.
"Sure, this is cool fun for me, personally, but are the other players going to enjoy the consequences of my trashing their relationship with the King?"
I concur. It is POSSIBLE to attempt to do anything in a D&D game. It is not always REASONABLE to attempt to do those things.
Some peopel cite RPGs as letting them unwind and do stuff they can't do in the real world.
I contend that in a "serious" campaign, the same social limitations apply. Yes, you can physically attempt to rob the king. However, you can do the same thing for the mayor of your real world town. But in both worlds, there are reasons we don't generally attempt to do these things.
As a GM, I try not to hard-code specific endings for the campaign (and the PCs throw the ring into mt Doom, the end.).
But when the players say they want to remove the goblin threat so they can extend their mining operations, I write material to present challenges to them as them pursue that goal. When so dork decides to do some stupid random activity that gets them all in trouble and completely throws out their goal, is that time wasted?
Some would say no. I think there's plenty who would say the dork acted stupidly and just cratered the campaign. I'd say its cratered if the campaign with those characters doesn't continue in as regular a fashion after that point (as in it peters out).
I'm all for the campaign changing directions through game play. I'm not for this happening through stupid game play, especially if its ends a campaign (thus contaminating my investment in my PC who's now locked in a dead campaign because of your actions).
I think there's some number of players who play their character as if they live there. They try not to act stupid, other than the occasional pun or joke, because they despise watching shows where the the protagonists do the stupidest things to make matters worse for the sake of plot (like not communicating which is the root of all comic book drama). Now take a party of those players and sub one out for a 13 year-old nephew. Who sees he has a 16 CHA and is a Rogue so he spends the rest of the game looking up girls skirts and trying to steal from every body.
That's the kind of player who causes trouble, in the stupid game play kind.
One way to describe it, is the player is breaking verisimilitude of the campaign. There's plenty of places for doing crazy, unpredictable things. Then there's times to not do stupid stuff for the sake of doing stupid stuff.
Kind of like how I hate in anime when they flip a character to a goofily drawn, large-mouthed, spazz. What the smurf is up with that? People like that should be the first to die before 1st level due to some orc attack or falling down a well.