Depends. if they keep it to disagreeing with the opinion and refraining from rudeness when doing so, then it is fine. When they start attacking the person holding the opinion, then it crosses the line into bullying. We've seen that a lot in F!S recently. There have been a few dogpiles that have started out okay, objecting to an opinion, but crossed the line into personal attacks on the person holding that opinion. THat is when it is unpleasant to read, even moreso when the people doing the attacking cloak themselves in a personal shield of righteousness.