They are aliens, so their mindsets are likely different to ours. That being said, unless they consider all plant life as being themselves (in which case why are they overgrowing/displacing earth plantlife?), and also do not believe that sentient beings should consumed (in which case the very act of communicating with them takes humans off the menu), then this seems unlikely. The possibilities for this though are pretty wide.
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They may consider all things equally edible and that not eating something that is dead, even if it was sentient, is wasteful.
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They may consider every living being a potential meal for something (including themselves), unless it does not think of itself as being food (ie, outside of nature), because they would consider doing so to so be rude.
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They might believe that deliberately killing lifeforms to consume directly or generate fertilizer is unethical.
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They may consider who or what gets eaten completely irrelevant.
Simply making them uniformly hostile with motivations that are always inherently destructive to humanity and the player is a cop out. Hostility in itself doesn’t really make them alien, it just makes them another one dimensional enemy mob. At the most, it makes their motivations only matter for tactical purposes, ex: spiking bags of fertilizer with weed killer and leaving it for them to find.
They are aliens, with alien motivations, values, and thought processes. We need to make them WEIRD, not just another implacable one dimensional enemy. We have enough of those already. They should be dangerous and difficult to communicate with, but not necessarily inherently hostile.