The difference is there will be two chains and you may not like what they decide to support!
That's exactly the reason people should keep their coins fully under their own control
offline. People not seeing the risk of this are either delusional, or they simply don't care - not sure what is worse. Seriously, how much effort does it take to install a proper client and to properly secure/backup your coins? Security should always be the main priority, but as it is very clear to me, a lot people greatly prefer convenience over security. One should never be at mercy of a central authority, which is exactly why people love the freedom Bitcoin is giving them. Unfortunately, not everyone appreciates that.
Essentially, people will only learn when things go wrong (i.e. them getting financially hit in the pocket).