Recently people have been discussing "mirror life" online, and the fact that it could very well be incompatible with "lefty life" (implying "lefty life is equally likely to be incompatible in exactly the same ways").
One possible outcome is that alien life does exist as I have stated (some kind of beachhead terraforming spore or some such), but that this life could very well be right handed as we are left.
Imagine that, that we get a communication from alien neighbors who moved in only to realize that actually visiting each other could result in widespread destruction just because someone breaths some gingivitis or whatever into the atmosphere.
I’m more inclined to think alien biochemistries would be so different from one another that they couldn’t affect one another for good or ill, and certainly one could not and most assuredly would not want to eat the other. If speculative silicon life forms existed, for example, I imagine to us they would be like living rocks, and nobody wants to eat a rock.
More speculatively, I wonder whether their arrow of time would be the same as ours. The block world picture of space time posits that the future exists along with the past, and we know that at the microscopic level processes are time symmetric, with no arrow of time. Could it be possible that an alien intelligence remembers the future? This was the theme of the sci-fi flick Arrival, which left any number of philosophical riddles to ponder include the old standby of free will.
Also, their metabolic rates and sense of the passage of time might be quite different. On earth flies live only about 24 hours, but that is from our point of view. What about theirs? I was recently reading that the reason flies so effortlessly escape our efforts to swat them is that because to them, we and our swatters and everything else move in super slow motion. Perhaps a fly, if it has a distinct temporal passage sense at all, experiences 100 years of temporal passage for the 24 hours we see? What if we found a world we considered dead, only to discover that its life forms move only once every hundred years as we count time?
All sorts of tantalizing questions about potential contact with an alien intelligences. It is often thought that we could communicate because of a shared common math, but this too has been seriously questioned, and it has been argued that alien maths could be unrecognizably different from our own. This might depend on how much we think math is discovered and how much we think it is invented.