You have a problem player. They can be made a non-problem player, though.
Specifically, you have one player who regularly says or does dumb things, and turns the game into an argument about the dumb things they're saying or doing. This may or may not be conscious on their part, but at some level, it's almost certainly giving them something they want. If you read page 6 of your DMG, this player is an Instigator. He wants to start things and make things happen and be the center of attention. Right now, he's doing that by sparking off arguments with the other players.
So, the trick here is to pull him aside, one-on-one, and call him on it. Then try to figure out between the two of you ways where he can get what he craves (that sweet, sweet attention) without tearing apart the group in general. Talk with your other players, and see how they feel about the whole thing. If you're lucky, the chance to be the center of attention from time to time in a way that isn't hostile will be appealing enough that he won't feel the need to hog the spotlight constantly by being disruptive at other times.
Essentially, your options here are keep going with arguing and roleplaying split 50/50, figure out a better way for him to get what he wants while not warping the experience for everyone else, or get rid of him. If you decide that you yourself are not going to accept the first option, that should give him plenty of incentive to help out figuring out the second.
Incidentally, if he likes the antagonistic attention, and he doesn't mind RPing characters who are destined to go down in flames, you might look into letting him play some of the villains for you sometimes. Give him the stat sheet, let him run the villain side of the encounter, and let him really ham it up, while you sit back, rest for a moment, and let yourself plan ahead a bit. The idea here is to find a way to let him channel these urges productively, while still letting the other players have enough spotlight that they aren't feeling left out. Reading up on the Instigator type and how to keep them happy would also likely help.