If you don't know, then don't say anything. Mods do not affect you. And modders have found ways to make it entirely personal so that they no longer affect your character, only theirs. If you didn't know about this, then now you do. There's very little excuse for anyone using mods to influence your character, so it literally shouldn't affect you in any way.
If this were a perfect world, then yeah. Modding the game, using add-ons of any kind, and engaging in RMT would be 100% problematic. But this isn't a perfect world.
There are stuff in the game that the devs haven't moved to resolve which the fans have. Deny the fans that experience, after so much feedback has been done around it, and you'll just alienate those players. Yes, I'm referring mainly to Hrothgar and Viera, but there are plenty of other stuff, not just cosmetics. For example, do you have any idea how limited and poor the colourblind mode is? I needed specific shaders to run content because the one setting I run the game on does not allow me to see ANYTHING in E9 and P3. Trying to clear those as savages was just hell. And sure. Shaders are greenlit by the devs. But they're still a third party tool I needed to use to bridge the system, and some add-ons do quite a lot of QoL things that the game really would benefit from without giving you an upper hand in combat necessarily.
Unfortunately, you're going to find quite a lot of people who aren't "100%" against them, because user experience is subjective and even the devs acknowledge things aren't so black and white. Yeah, by all intents and purposes, using those is against the rules and you shouldn't use them. The reverse side of the coin is that there are people who will use them to enhance their user experience in ways that aren't invasive to others' experiences. Doubly so when the devs take a long time to meet feedback.