If there's one thing I've learned in life, is to never listen to people moaning about the "good old days" and how [insert group] has "ruined" [insert place], not like those [other group] that were great. The good old days were never actually that good, and [insert group] is neither worse nor better than [other group].
We're all way too young to be curmudgeons yet, so stop acting like it.
It's also amusing to see one wave of gentrifiers shake their fists angrily at the next wave of gentrifiers. I heard about the Yuppie Eradication Project - where people who invaded a traditionally Latino stronghold vowed to key the cars of people who later invaded that.
FWIW, they can fight for the Mission all they want. No matter how many rose-tinted pairs of glasses you put on, it's still the piss-filled, shit-littered, gun-happy, knife-stabby, gangbanger-filled shitpot we know and love.