There is debate within the scientific community about changing other planets in general. Not everyone is convinced that we should alter or terraform to suit our needs.
This is like nimbyism on steroids. "No one build anything what if there is Rare Science in our backyards".
I mean yes I do kinda see your point, but priorities man. There are ridiculously large advantages to colonizing the universe and destroying a few samples is a low price.
It's not that we can't or won't. It's that we should study and debate it before we do anything to change the environment. Given how humans have run roughshod over so many environments, I think carefulness might be warranted.
Particularly when we don't even know have reason to believe there are samples. If/when we detect life elsewhere we can talk about leaving it alone, but there are plenty of rocks in the universe with no life that we can work with.
Why is contamination a question? there are millions of rocks scattered around that are not contaminated or explored. There is more to learn by contaminating a few and seeing what happens than to leave them all uncontaminated.
Some related links:
https://planetaryprotection.nasa.gov/intpolicy/
https://www.astrobio.net/mars/should-we-terraform/
https://en.wikipedia.org/wiki/Ethics_of_terraforming