First, the Iranian state does not have a policy of finding and murdering gay people. You'll note that basically all press reports of the execution of homosexuals ultimately refer to acts of rape, possibly statutory. The argument, roughly, would be that this is a pretense, and certainly, Iran's legal system is very flawed, its laws regressive and offenses such as "enmity against god" ill-defined. Nevertheless, they are not ISIS, and merely being homosexual is not a crime.

Second, if you want to morally justify sanctions based on the idea of improving LGBT rights in Iran, find at minimum some evidence that there is significant percentage of those people in Iran who would welcome them.

Third, Saudi Arabia (see [0]). The west simply has no, absolutely no leg to stand on when it comes to the human rights argument. It is blatantly obvious that Iran could continue as it does with regard to its treatments of minorities, so long as it stops opposing our geopolitical interests, and starts to provide some benefits instead.

To summarize, this is not an issue of moral relativism. This is an issue of dishonesty and jingoism.

[0] https://www.out.com/news/2019/4/29/saudi-arabia-kills-5-afte...