Very real concern. A lot of effort goes into sterilising craft intended to land on or impact other planets. If we fail to do so, we run a real risk of seeding earth life on those planets and forever ruining our chances to test them for the existence of life prior to contamination.
The prioneers and experts of the field see it as a problem. The uninformed opinion of the general public doesn't carry much weight on this matter.
People who don't see it as a problem should take the time to read one of dozens published papers outlining the dangers and problems it will pose. If they then still don't feel it's a problem, they're encouraged to publish their own research supporting that view.
Some do and some don't. In terms of knowing about life on other planets of course it would be ideal to maintain planetary quarantine protocols and so on. The problem for exobiologists is that given the absence of visible life in our local system, any life that does exist is fossilized or fragile, and of course we would want to approach it with the same delicacy that we would any other fragile thing.
On the other hand, our solar system is but one among many and the longer we hesitate in exploring this one the longer it will be before we are able to explore others. TAn excess of caution can become an excuse for inaction. If earth is an oasis in a planetary desert, the way to find other life is not by maintaining extreme caution about disturbing the surrounding sand dunes but by trekking across them in search of other oases.
While not everyone likely sees seeding Earth life on another planet as a problem, I think most would want to know if life existed there prior to that, since it helps us answer quite a few fundamental problems.
I'm not sure why I used "problems". It's obvious to me I meant "questions", so likely I just misspoke. Knowing if life exists elsewhere at at certain minimal levels answers some fundamental questions.
