Universal Common Descent (UCD) is NOT a strict requirement of mainstream science or evolution. This is just one hypothesis that is subject to revision.
Scientists regularly consider the possibility that life arose multiple times on earth.
Also remember that many scientists are hopeful we will find life in the far reaches of outerspace (e.g. SETI). Whether this hope is well placed is a debate for another day, but the important thing to remember here is that any life outside our solar system would almost certainly be from a separate origin event. We would not share common ancestry with them.
So while we regularly use the terms Universal Common Descent (UCD) and Last Common Universal Ancestor (LUCA), this is just one hypothesis among many. Alternate hypothesis are considered all the time by some scientists. Now, there is some evidence (certainly not definitive) that all extant (still living and not extinct) life on earth shares common ancestry. But given that we do not know how important convergence is in abiogenesis, it is not clear how to assess and interpret this evidence.
In conversations among Christians, the correct place to focus is the common ancestry of humans and the great apes (gorrillas, orangatangs, and chimps). The evidence here is overwhelming for common descent (genetic data, intermediate fossils, etc.), and this also where most of theological discomfort arises. The focus should be here. If we resolve/understand this evidence for human evolution in light of our theology, the rest is just a side issue.
Frankly, most people who argue against common descent just bring up UCD as a red herring. It is an excuse to argue about foggy details of microbial evolution. But who cares? Even if we grant that evolution just happens within “kinds,” we are left with the same question of human evolution. Looking at the evidence (genetics and fossils) it really looks like we are the same “kind” as the great apes.