I didn't say it should be banned, but I think this is not a very good defense for just about anything:
It would have to be pretty targeted because that’s how the rest of media works. Magazines, newspapers, cable television…. It’s an age old model you’d be fighting.
You cited three age-old institutions that had their legacy business models destroyed the very moment consumers could escape them.
I already barely use discord (after all these years I have only joined two servers, and both make my eyes bleed every time I look at them) - and I can get along just fine without those communities if they make it the tiniest bit less pleasant for me as a consumer.
The only reason I use it at all is for a small number of niche communities that aren't very active elsewhere. My life would be nearly exactly the same as it is today if I never visited those communities again.
Not in a million years will I pay for discord, and if their ads can't be blocked, they better be damn near invisible or I'm out. Considering I've never heard one person say how much they enjoy using Discord, I feel confident there are a great many others in the same boat.