Science

I think it makes sense to reason from what we know about physics and chemistry. We say there's "carbon based" life because carbon facilitates a snap-on structure that makes it the basis of molecular chemistry we use for DNA and proteins. Sometimes we look at other planets and hypothesize other pathways to life based on plausible chemistry. You don't have to assume life is going to be like us in order to have your reasoning about life in the universe being based on plausible mechanisms known to science. That's why we look for planets in what we think of as plausible habitable ranges, we look for water, we look for chemical signatures of metabolism along known pathways.

Of course, always be curious about new possibilities, but weight what we know. There could be life in forms we've never imagined, and we should be open to that. But for now, knowing that organic chemistry, the building blocks for DNA exist and might be widespread is in and of itself a reason to think life could have emerged elsewhere, even though it's only reasoning from the familiar example we know.