Honestly that seems even more far-fetched. Visa and MasterCard are essentially a duopoly. Where on earth are customers going to flee to on bad pr?
1. Customers in e.g. the EU may push their reps to "do something" about two US companies controlling all e-commerce.
2. Customers frustrated that Mastercard have gone on the record as refusing to block payments to terrorist-supporting orgs while refusing to process payments to look at titties may pressure regulators to start having a much closer look at Mastercard's money flows.
Both of those seem like meaningful concerns.
Regulators are much more on the side of MasterCard than they are on the side of disgruntled pornography customers.
99% of normal people find cryptocurrency strange and inscrutable, and if you think otherwise you're in a bubble.