Also worth remembering is that we cannot know if this is the only universe. There could conceivaly be as many different universes as there are atoms in this universe, all with different parameters and rules and relationships between different bits and pieces.
There could be many where life cannot exist because those rules are set such a way that complex structures cannot form, there may be other universes where just one constant is different (say, the gravitational force) and that could lead to very different conditions but where forms of life are still possible, but that would look very different to those we have in this universe.
It's all totally unknowable, and without that knowledge it's foolhardy to declare firm beliefs on anything other than those things which we can directly or indirectly witness. We can all have opinions based on what our best guesses are, but to try and impose those opinions on others or to claim any sort of priveleged knowledge based on them is what gets met with resistance.
Even from a scientific standpoint, to say we understand the universe would be a bit like standing ankle deep in the surf on the north east coast of Australia with a telescope and a sonar machine and whatever other equipment you can imagine, and declaring that we understand the entire Pacific Ocean based on the measurements we can take from that beach in under a minute. Which is why science always says "our best understanding with the information we have is....." (often unspoken but the subtext is always there)