In a "just for fun" session of the card game Munchkin, would it be okay to join a game in progress? Of course the joining person would be in a disadvantage.
Arguments against this, as far as I can think of for now:
I've played plenty of games where someone has joined mid-game, and it has worked very well them just starting as if from scratch (i.e. at level 1 and drawing the starting hand of 4 treasure, 4 doors).
In my experience, what tends to happen is the established players have no problem with helping them to fight monsters they can't beat, meaning they'll level up and get loot just fine without needing a level boost.
In terms of changing the play order, I have a feeling there's a card which influences turn order in one of the early expansion sets, something along the lines of "Player is now fighting this monster, and play continues as though this were the player's turn", effectively skipping everyone in between - although I can't find the card name or text with a cursory search. Also, I wouldn't have said Munchkin is a game which particularly relied on the turn order, so I don't really see how this could be a problem.
In my opinion, if someone gets upset over a new player joining mid-campaign in casual play, they're probably taking Munchkin too seriously.
If it's "just for fun" and everyone is still having fun, then sure. If someone finds their fun level jeopardized by, for example, the disruption of the play order, then either you should delay the introduction of the new player or change the mind(s) of the opposed player(s).
Does it make sense: That depends on how long the game has been running. If you've only been around the table 1-3 times the disadvantage isn't so massive that the player has no real chance of catching up, more than that it doesn't make much sense to join games already in progress.
Is it okay: That's up to the people playing the game. There's no major difference from adding a player, some things would have been different if the game had started out with 4 people instead of 3, but those are made up for by the disadvantage the new player faces by coming in late. The turn order is disrupted, but the new player gets none of the benefits or detriments of having been in turn order until now. The best place to add a new player to the game is immediately after the current player, so they get into the game and start their catch-up immediately.
Would it be okay to join a game in progress? If everyone at the table is okay with it, of course. I have played dozens of games where someone or multiple people have joined late, I would restrict new players only if the end-game was clearly in sight.
Some arguments against:
Player order. If someone believes mixing up the player order is a game breaker, they leave too much up to chance rather than strategy. It is just as likely they will be positively or neutrally affected by the new player order as negatively.
New player will ally with a particular player. I've had people invite their friends part way through and this I was apprehensive, assuming they would just assist their friend to victory. Often they are even more competitive with their friend and if they are a good player will be persuaded by good arguments for coordination rather than blatantly helping their friend.
End-game is in sight and new player has no chance. I have joined very late and still won games. But if the end is only a few turns away, the new player will only be able to throw their weight for or against one of the contenders. This leaves a sour taste in the loser's mind, even if they may have ultimately lost anyhow.
New player needs to be taught the game. I am fine teaching new players at the start of the game, having a new player come partway through upsets the flow and may detract from other's fun. Best to wait until next game.
Inserting a new player into the turn order is far less consequential than the change in balance of power that a new player introduces. Most games of Munchkin I've played come to a series of showdowns in which one player tries to win and the other players try to stop that player. Players too far behind have a much higher risk of kingmaking to end the game rather than trying to win.
Given that, the question is whether a new player added at that point in the game has a reasonable chance of winning. You may want to have them start at a level higher than one (such as the lowest level any other player is), and possibly draw a few random pieces of equipment if the game is reasonably far along.
