Most of the resistance to it on Reddit was because NSFL content was technically not allowed on the site at all and adding a specific tag for NSFL material could be seen at legitimizing it. But they didn’t heavily moderate it either so I don’t see the point in refusing a tag for it if they’re not going to do anything about it themselves either.
What really blows my mind though is the subset of people that want a NSFW tag to mean Gore/Death and a separate PORN tag for titties and such. I mean, we already have established terms for those so why not stick with what everyone already knows them by?