As a PvE player in all MMORPGs I have played, I welcome the change which Aion will present in molding PvPvE. Sure, the Abyss is an open gank arena but you get rewarded extra XP from the higher grade monsters and gain AP in the process to purchase high-end gold gear. It's not like they're throwing you to the dogs while offering little rewards so you may as well make the best of it when you make an appearance.
Rifts are typically announced when they open and when they do open, it's only for a limited time and once the invading player dies and the rift closes, they don't respawn in that location. This does not happen in the starter zones.
Not to mention, the classes are fairly well balanced if used by the right player to their full potential. Hell, most people who tried the Assassin got mad because they expected it to be like WoW and you could stay stealthed for as long as you want. Most of the QQ going on in the boards about classes is the same reason you see in any other MMO: terrible players who can't pvp and want to be spoon fed by screaming nerf [class].
It's always been pushing itself as a PvPvE title so I don't know why people are shocked when they discover you will be doing PvP. Heaven forbid your pixels reach 0 HP.