DMing is a delicate balance between all the players expectations vs what is the story the DM is trying to build with the players. A good DM must learn what are his players' expectations and motivations for playing the game. I've had some group where a one short combat in a long 8 hours session was more than enough and others where combat was non stop. Both were to be DMed very differently but the end result was that everyone was having fun.
Yeah, ultimately if everyone is enjoying themselves, then mission accomplished. What that means will vary from table to table and person to person, so any GM and group of players need to kind of figure out what works best for their specific game group.
Now, there are players that can be disruptive to a game. They must learn that there are consequences to their actions. They either have to live with these consequences or simply stop playing with their current group (especially if they are the only ones with such a behavior). The compromise thing is not for the DM alone. Players must learn that what they like might not be the same thing as their co players.
I think compromise is definitely needed, and that both parties need to consider it. I think the question of consequences is a little trickier. I think that consequences for a player and for a character are different things.
If a player is disruptive in some way, I don't think that's something that should be handled in game.....by punishing the character in some way (killing them, imprisoning them, taking away items, etc.). Such an action may not actually address the problem. You need to talk to the player about what issue the player has that caused the disruption. Otherwise, you're treating the symptom.
Likewise, if I as a player decide my character is going to try to kill the king, I should expect that there will be consequences for my character. I do agree that if you choose to have your character do something reckless, then be willing to have them face whatever the consequences may be.
I think some suggestions in this thread are advocating for punishing the character as a way of correcting the player, which I don't think is a great idea.
In the case above, one player was bored to the extreme and decided on his own to take matters into his own hands. That was a disruptive behavior and the consequences of his actions should've been made clear from the start. If the player was aware but "went" with it anyway, then the character should die. If the player was not, then the player should have the option of "withdrawing" his actions as if nothing happened and without consequences. If he decides to press on, even with the knowledge of what is to come, then he should be screwed.
I don't know if it was disruptive behavior....or at least, if it was disruptive, I can see why it might be justified. A bored player is an unengaged one, and so the GM should try and re-engage them in some way. I spend a lot of time GMing, so when I get the chance to play, I'm a very patient player. I'm willing to let the GM do their thing, and hope that I'll be rewarded with some engaging play. I cut the GM a good deal of slack. But...I have my limits.
Generally speaking, I'd address this in some other way. I might say to the DM "hey, when will we see some action?" or something like that. I play with close friends, so we can level with each other like that. Ideally, a table will have some means of having discussions like these, and so if a player is bored to the point they're about to have their character do something rash, they have some way of addressing it before is spills over into play.
The first step is to recognize there's a problem. It's not always easy to tell, but very often I think it's pretty obvious when one or more players are bored. If that's the case, then you have to do something about it. It may be something as drastic as reevaluating the entire campaign.....or it may just be as simple as have some bad guys show up and a fight breaks out. It really depends. I'd start with an easy solution.....some bad guys showing up and having a battle.....and only move on to more serious solutions if needed.
All in all, I think that this campaign or playstyle isn't a great fit for this player. I don't know if killing his character will actually help anything. He'll make a new character.....and very likely be just as bored.