Colonization is only ugly if someone is already there to begin with
And outside of maybe some microbes (mostly likely fossilized, if that),
nobody is on Mars besides red rocks.
And if it comes down to human survival or protecting a few bacteria,
guess who is going to win.
If you feel bad about losing some microbes, then you must have a
fit whenever you scrub down your kitchen counter or sterilize a needle.
Besides, if we do find tiny life on Mars, they will no doubt be preserved
by science and probably do better than being stuck on their own planet.
It wouldn't surprise me if any microbes put in that chicken soup container
in the Vikings proliferated, at least for a while in that one spot.
In summation, stop putting old Earth politics on exploring and colonizing
outer space. The rules do not apply.