People aren't mean, they're just stating a truth about uke's personality. I think that seme is quite irritating because he's too forceful with his advances and he's imposing himself on the uke, but he truly believes it's a right thing to do. Although I don't like his actions, he's at least straightforward and sincere. I think you've answered your own question. It's not about the uke's refusal, but it's about the way he did that. It was unnecessarily harsh and hurtful.
I'm inclined to believe most people who comment haven't been in relationships themselves, sooo yeah ╮(￣▽￣)╭
I don’t think everyone should be so mean towards the uke. True he could be nicer in saying that he doesn’t wish to be with the seme but how is him not wishing to be with him just because they became mating in the middle of his heat (which makes it hard for alphas & omegas to think properly) an asshole? And i think the uke may have been through some hard times. People just need to stop with some of these comments smh.