Sounds weird to me. Pretty sure that they legally have to make sure that they don't host illegal content. Or does "NSFW" enable some kind of end-to-end encryption?
You don't have to take my word for it, just check it yourself, although it seems that this week, they renamed the NSFW setting to "Age-Restricted Channel" (in preparation for this change, no doubt). The verification-related portion of the behavior I described was implemented for the UK months ago.
The description still contains: "Age-restricted channels are exempt from the explicit content filter."
EDIT: IANAL (or american) but if Discord was policing content for legality rather than age-appropriateness, wouldn't they lose DMCA Safe Harbor protections?
Wait! This does not mean they do not scan it. What I understand from that statement is that they filter explicit content, as in they prevent it from appearing on the user's screen.
When you enable the "NSFW" mode, you tell Discord "it's okay, don't filter out anything". But Discord probably still scans everything.
So that makes sense to me: if you don't validate your age, then Discord will not allow you to join channels that disable the "adult" filtering. I can personally live without adult content on Discord...
They can read everything that you send already, if your problem is that they may filter something that they consider NSFW and you don't... well I am not sure how big of a problem that is.