1. Gain of function research primarily uses samples collected from nature, and seeks to stimulate their evolution in as natural a way as possible to learn how viruses evolve in nature. If such viruses were to escape the lab, they would appear "natural"
2. It's not xenophobic for people from the US to suggest the possibility of a lab leak, because the US was itself funding gain of function research on novel coronaviruses in the Wuhan BSL4 lab
3. Lab leaks happen more often than most people realize[1]
[1]https://www.vox.com/future-perfect/2019/3/20/18260669/deadly...
There is, from my understanding, reasonable evidence to conclude the virus was not engineered from the perspective of "we took genes from one virus and moved them to this virus," but there's no evidence disproving the idea that it was the result of gain of function research.
My personal feeling is that these statements are true:
* The virus is unlikely to have been engineered (in the way I described above) and leaked.
* There is circumstantial evidence the virus was the result of gain of function research and it leaked.
* There is circumstantial evidence the virus was a natural research sample and it leaked.
* There is circumstantial evidence the virus was introduced by an animal/person who traveled to the wet market.
Some of these are more likely than others, and an individual's own calibration for what is likely or unlikely will probably come into play more than evidence in the short term and possibly long term as well. I can say the vast majority of us are not qualified to answer the question either way though.
WIV had recently published research on, and had an active grant to perform (at the time of the outbreak), chimeric Coronavirus research, and they were one of the two world leading labs in this. In that research, they were transplanting the spike gene from one virus to the "backbone" of another. You could call this "engineering" or "gain of function" depending on your perspective.
The thing that raised people's suspicions about this is that the spike RBD strongly resembles a virus sequence they released recently (Pangolin-CoV), and the backbone strongly resembles another virus they recently published (RaTG13). That suggests that there was some sort of recombination event. That recombination could have occurred in nature, in an animal that was simultaneously infected with two viruses, or it could have occurred in the lab.
Incidentally (or perhaps not?), there is some evidence that the furin-cleavage site is what makes the virus resistant to hydroxychloroquine, which can be countered by combining it with a TMPRSS2 inhibitor: https://journals.plos.org/plospathogens/article?id=10.1371/j...