We all come from different backgrounds, with different points of view and ways of looking at the world. But, there's one thing we can all agree on: no one likes a toady.
LeFou seems to exist solely to tell Gaston how awesome he is and cheerfully get beaten up whenever Gaston needs a punching bag.
He's kind of a stand-in for the whole village that way: a community full of people who live to bask in Gaston's glow and are so awed by his strength and good looks that they can't see how horrid he really is. LeFou quite literally takes punches with a smile on his face, willing to suffer any indignity as long as it comes from Gaston. He's even happy to freeze solid outside Belle's house just because Gaston says so.
Genuine devotion? Simple fear of a pounding? Not even LeFou may know for sure.
That makes LeFou a strange sort of comic relief—like Cogsworth, if Cogsworth's yes-man tendencies broke loose from their handlers and ran amok. We laugh at his pratfalls and general foolishness at being a willing part of an abusive relationship with the town bully. For the first two-thirds or so, it's all kinds of funny. But, the turn at the end shows us just how awful a toady can be. Since LeFou never questions Gaston, he's all too eager to join the mob marching on the castle.
Hey, Gaston wants it, and if Gaston says it's the right thing to do, he's more than happy to play along.
Like any good toady, he's happy to graduate to bully status once a weaker target presents itself. The battle at the castle sees him turn into a real monster, threatening to melt Lumiere down with a torch and otherwise acting like a world-class sadist. For the crime of siding with Gaston to the detriment of everything else, including any semblance of human decency, he gets to share Gaston's humiliation. We suppose he can take comfort in the fact that he doesn't plummet to his death like Gaston does.
But, what else can you expect from a guy who lives to take abuse like LeFou?