Most likely exterminate us no matter what the environmental impact
If the aliens have FTL capability, then we stand a chance of their being benevolent.
From what we know about physics, FTL capability isn't likely.
Which means they come here, it's a one way trip.
And nobody would come this far one way without planning on it being a colonization venture. Which means competition for resources.
Which means war, and whomever wins wipes out the losers.
Since they came here, and are in space, they have the technological advantage AND the high ground.
Odds are we'd lose, fast and badly.
Biggest reason I know of to support ALL space exploration, development, energy, and propulsion technologies; governmental, corporate, and private.
Otherwise, we're likely to all end up like the Tano.
Gone.
