Seriously, there are very, very limited instances whereby a team switch is OK.
1. Your team up and moves to a new town. If this happens, it's not like you're switching teams, but your team switched on you. I was a Houston Oilers fan back in the day and then they moved to Tennessee where I had no attachment. I simply was not going to root for a team based in Tennessee (I was born in Houston). Living in South FL, I became a Dolphins fan for the same rationale as why I originally became an Oilers fan. The Oilers switched on me, but I'll still rock a throwback Warren Moon jersey.
2. Your team drafts a dude like Jameis Winston #1 overall. I get it. As a Miami Hurricanes fan, that may be too much to bear. I don't even want to think of what that'd be like for Canes fans who had to deal with that.
3. You're gambling on a game between two teams and for 3 hours you root for where your $ is.
Other than that, I just think it's a bandwagon, frontrunner move. No one ever just stops being a fan when **** was good and jumps to a crappy team. Nah, they run to the Patriots or whatever the hot team is like fan mercenaries.