The flaw is that crypto was supposed to be better than fiat.
Any attempt to say they are on the same level is intellectual bankruptcy.
Like asking "What's the problem with restricting access to VX? Everyone's got a can of bug spray in their cabinet and they're both organophosphates, brah!"
The big narrative I keep hearing about bitcoin the past ~8 years is that it's no longer considered a currency even by the true believers.
There's certain medication that's cheaper for me to buy online from overseas than it is in the US (where I live) even with my insurance. Those from whom I've bought it only accept payment in Bitcoin. I'm going to admit that it seems kind of sketchy, but I'm grateful for the existence of BTC because of it, and I think it really does seem like a good decentralized currency in that situation.
Maybe skeptics would label this money laundering or criminal activity, but I'm using it to buy medication I have a prescription for; if this is illicit, it feels like it shouldn't be.