What's keeping humanity in Trek from exploiting other cultures is the fact that Earth and its colonies don't need anything from a less advanced culture.
This wasn't the case during TOS. We saw the Federation trading with very primative cultures for their "rocks."
The Hortas could not possibly be considered a technologically advanced society, there was no suggestion that Humans would leave the Horta planet at the end of Devil in the Dark.
And how advanced were the Halkans really?
Or perhaps it is the fact that the Federation no longer has a monetary system. There is no need to exploit other worlds as they don't do things for financial gain anymore?
The thing about Avatar was, the primary purpose behind extracting the natural resource (the floating rock) was to take it to Earth as a new power supply. Yes the company doing the extraction was going to get rich in the process, but the people of Earth would also benefit. Earth was "dying," a new source of power was desperately needed.
If the Federation were "dying" and desperate enough, you bet they would have up rooted a few trees too.
"Avatar" is like a better done version of "Insurrection."
I think the opposite, Insurrection wasn't as heavy handed as to who were the good guys, and who were the bad guys. There was a degree of uncertainly, allowing the audience to decide for themselves. The execution was flawed, but the story itself was better.