Thanks. No-one likes slavery, and often villains try to justify their actions in their own mind as to why their own villainous actions are acceptable. The Guardians could be fighting against enslavement (not just of them but others in the galaxy) and would never accept the Collector's reasoning.
The Collector would of course accuse them of being short-sighted and not seeing the full picture. But really, would anyone here simply accept a lesser evil - eg killing 100 people to save a million - over a greater evil without trying to find another way first, especially if say your family or friends are in those 100 people?
I think the Collector could offer a great opportunity to allow for some Star Trek-type moralising and debates. Maybe one of the Guardians would stand in the Dr McCoy position and want to save everyone from mass abduction simply because it's wrong, whereas someone else (not sure who) could stand in the Spock position and think that perhaps there is some merit to the Collector's methods if you think about the greater good. Then you could get someone representing Captain Kirk who could see both sides of the argument, but ultimately agrees that mass enslavement is wrong, even if it means jeopardising the future and allowing the possibility of Thanos to be completely victorious.
So yeah, I think the Collector would add a real depth to the movie lifting it beyond just another all-action sci-fi flick.