If we are, in fact, alone in this universe, there are two ways to look at it. First, the way you concluded: "it would behoove us to take good care of each other and of the planet we call home"
From another perspective, in all of those trillions of stars out there, if we are alone, then we are such a small component of the whole as to be completely insignificant. We are a tiny spec of dust to brushed off and never thought of again.
I don't know the source for this one: "Either we're alone in the universe or we aren't. Either possibility is mind-boggling."
Personally, I like the theory that we're a bunch of tiny Whos or mere 3-dimensional creatures who are incapable of understanding what's really going on. We may also have a ridiculously fast sense of time, and the Elder Gods or whatever work on such a long time scale that nobody around here can tell that things like the speed of light are very slowly changing.
I also like the theory suggested by Anne Elk at Daily Kos: "Watching the dominant species self-destruct on planet after planet may be God's version of Breaking Bad."
[Subject line is obscure reference to Billy Wilder's One Two Three (1961).]
There's a great book by physicist João Magueijo called Faster than the Speed of Light (2003), which proposes that considering C to be a slowly-changing variable rather than a constant solves a number of cosmological questions. The book also tells you what a "cosmological question" is. Faster is written for non-physicists and includes how the author got into theoretical physics in the first place, what he was doing when he got his flash of insight, and is a marvelous exposé of modern academia -- especially the sciences. Those parts are hilarious and depressing at the same time.