It is definitely not a bad thing when high income people move into a low income neighborhood. While some people may get displaced, and certainly that isn't fair to them, high earners bring a lot of things that cities need. Two things stick out: firstly, they bring money, and second, they demand security. Many of the inner cities in the US are severely lacking in tax receipts, which affects poor people way more than it affects rich people. Rich people can afford to get their own streets cleaned, send their kids to private schools, pay for trash pickup, etc. Poor people need municipal government to do all of this for them. As municipal governments can't print money (and especially in these times can barely even borrow money--the municipal bond market is in absolute shambles all over the country), the only option they have is to raise revenue. "Gentrification" (I don't like that word, because it has become a derogatory term for an undeniably good thing) is one sure fire way of collecting taxes.

I'm definitely a gentrifier, and an unapologetic one. I pay Detroit around $6,000 in taxes every year (and this doesn't count all the indirect benefits of spending money in the city), which is probably more than 99% of the population here. That money (when it's not going to grease the wheels of some sleazy bureaucrat) helps my neighbors' children get an education, funds the water and electricity that they all enjoy, helps repair roads, keeps the buses running, and on and on. Above all, we don't tolerate crime, and we will badger the police to keep the place safe. It works, as at least in Detroit, the rise of the gentrified neighborhoods correlate perfectly with a sharp drop in crime, despite the fact there are still a lot of poor people around. Should people like me stay away from inner cities because some small groups of people may be uprooted?