Here is example scientific paper that studies aggressive behaviers based on genes in animal and humans: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4092042/
By studying Thargoids species one can try to determine how agressive are this species and look for alternative ways of dealing with them. It's real science.
But you need dead and live speciments for that. This is why i find it so bizzare that so much lore about Thargoids is just pure guess work, since no one in 2nd War even saw a live or dead Thargoid species.
Are you seriously saying that you want to do some DNA tests on dead Thargoid bodies in-game so that you can prove that you didn't derail this topic? ^^
Linking a science article that , yet once again, has nothing to do with the topic to give some "credentials" to what you are saying is also a pretty weird trick, but that is indeed used in most of pseudo-science areas...
Most of what we know about Thargoids is simply not know to the general public or anyone not actually requiring this access to work, there is nothing strange about that. Each super-power, each Warlord and each faction would love to get their hands on Thargoid stuff to get informations that the others don't have, and would therefore protect and hide any information they posess about it.
I'm more surprised that we didn't get an encyclopedia full of errors or false rumors as an information war.
So, how does that takes us closer to have a definitive answer with the information we currently have and no speculations on which one is the most violent as per the topic title?