One of the arguments against homeschooling is that children need to be able to learn to deal with opposition while young. I agree. That's why I often tell my little ones "no". ;)
Seriously, there are those who forward this argument who even seem to think that it is a good thing for a child to have to face bullying because that's just part of "the real world". I'm not quite sure what real world they mean--adults generally just escape from bullies (unless they're stuck somewhere like prison) or take them on (which could end up in prison for them, so it's not a great solution in most cases). Most people will simply do what they can to get away from someone who is abusing them.
In my experience, when someone has been subjected to repeated abuse from which they cannot escape, they usually end up with serious emotional and mental problems. According to a recent study, children who are repeatedly bullied are more likely to develop psychotic symptoms in early adolescence (Medical News Today website). So, to those who think parents are harming their children by taking them out of school for bullying issues, which is the greater harm--a couple of years at home with mom or dad or teenage psychosis?