Fictional: Complain that flying mounts would kill the game, making it an empty shell where the land will feel seamless without seeing players running around.
Reality: Sees hundreds of players running around, each doing their specific thing, not caring one bit about others, not waving or chattting, even in shout, except for the stupid raise call because that person didn't select the map's Aetheryte in case of.. ? (not including gil sellers)
To me, I've come to terms with MMOs. It's a very fake attempt to tempt people into the MASSIVE crowd, fun to interact with. <-- selling dreams
Option to get over that feeling: FC, LS (Guilds, etc) Stay in one that will make you feel there is true human beings behind these pixellized characters.
The rest is just Soloing, and forced parties so that solo player can complete content.
*OP - Flying mounts or anything won't kill a game or making it empty: It's the people behind their screens that does. (or not, wishful thinking

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If they make a flying mount (Voidal anyone?) please make it so we can fly for real.. this mount feels soooo slow.. >.<
**What makes me stick to MMOs: The skill animations (specially of Magic-Users), the Story somewhat. Questing, some grinding, Achievements (gotta catch them all! ^^ ) and - The people that you enjoy spending your dedicated time into gaming.