I think this question is too given to speculation to make for a good debate, but it still interests me.
Basically, Star Trek's heroes must abide by the Prime Directive, an order that forbids them from interfering in the affairs of primitive civilizations. Hardcore fans could probably argue it's more complicated than that, but let's assume it is this simple for the sake of this thread.
I suppose you could make two basic arguments in favor of the Prime Directive: an argument from utility and an argument from principle.
The argument from utility would contend that interference in alien cultures - no matter how benevolent in intention - will likely backfire and cause more problems than it solves.
The argument from principle would contend that interference in alien cultures is wrong simply because a species has a collective right to self-determination and unfettered development. According to this line of thought, there is something intrinsically desirable about a species charting its course without the guidance/influence of extraterrestrials.
But, if one were to adopt a policy of strict non-interference vis a vis primitive alien civilizations, one would commit oneself to the following:
-Permitting genocides and highly destructive wars.
-Permitting plagues, disease, general poor health and misery
-Permitting extinction events
It seems that although the Prime Directive has good intentions, it could result in unjust outcomes, at least some of the time.