He liked Belle, when the rest of the town said she was weird for reading.

He thinks she’s weird for reading too, he just thinks she’s pretty enough to make up for that “oddity”

He’s clearly respected throughout the region.

He’s feared because he’s the strongest and has money

The beast (after being cursed for being a dick to strangers in need) did kidnap an old man and then did a prisoner swap for a girl he intended to groom into a sexual partner

Gaston wants to make Belle quit all her reading and tinkering and inventing and turn her into a breeding sow

When the kidnapped man returns to the village and everyone refuses to believe him, Gaston does and leads the charge to rescue his daughter.

He pretends to believe Belle’s dad initially to manufacturer good will, then tries to murder him in the woods in an effort to get rid of the last roadblock keeping him from Belle. Failing that, he uses his “influence” with the town to have Belle’s dad committed to an insane asylum (without any semblance of a trial) when he comes back and accuses Gaston of murder. He doesn’t believe that a beast had kidnapped Belle until he sees the magic mirror.

The fact that Belle was successfully love bombed and groomed doesn’t make Gaston wrong for coming to rescue her from this rich noble that was kidnapping people.

Gaston incited a riot, an honest-to-goodness grab-your-pitchfork-and-torches mob, to retrieve what he viewed as his property. Yes, the beast is a spoiled, bratty, sexual grooming noble, but Gaston is also a massive piece of shit dude.