People are going to be (too) greedy or not, regardless of whether guild-tagging exists. Lowering the personal cost of leveling has nothing to do with human nature.
In fact, guild-tagging lowered the potential profits of the 'too greedy' people. Prior to tagging, everyone needed their own copy of 'must have' gear, or suffered with horrible efficiency. This led to a wealth flows up scenario as you purchased the good sets from the near-EOC crowd, even more so than currently exists.
Guild tagging didn't just lower the cost of 'hunting' it lowered the cost of everything.
'Suffered' with horrible efficiency, really? So what, you think the scenario we have now with everybody and his freakin grandma wearing the exact same thing, reading from some list of items that we're supposed to wear, double checking with the FSH, 'just to make sure', is better?
RE the wealth flows up scenario, the very fact you even think that is just another symptom of the 'I want, I need and I expect' society we have now. Who's to say everyone is entitled to the best gear for as cheap as it can possibly be? When I first started this game, people would use what they could 'afford' to use in order to 'hunt' or SE hunt. Sure we wanted the even better gear but we either had to WORK for it or donate our asses off. THIS was actually even after guild tagging too. Eventually though, as all the guilds slowly built up their tagged stockpiles of the good gear all of it's value plummeted, it's desirability completely destroyed.
Do you know what HCS' idea for a fix to this issue was? Let me tell you, they brought out more and MORE powerful gear, that's great! Isn't it? In my own honest opinion no, it's not great it's the exact opposite of great.
Do you remember Grimnok when it was actually an achievement to put together a 1-hit setup? When BigGrim used to say that this game wasn't intended to be that way, us sneaky players found a way to do it though. Now, well now with all the super potions, mega gear and overpowered relic bonus's it's actually hard to NOT 1-hit...
It's a sad, SAD state of affairs to be in.