This has been a problem for a long time and unfortunately the outrage around the duopoly died out the last time we confronted it, which was in 2010 when Visa/Mastercard blocked Wikileaks (https://www.forbes.com/sites/andygreenberg/2010/12/07/visa-m...).
It's trickled into other mainstream/downstream services as well like Patreon. Patreon bans certain creators because they have a "policy" on acceptable content that is backstopped by visa/mc policies.
It is still a problem in 2020. Gab was recently impacted by Visa blacklisting them (https://news.gab.com/2020/06/19/gab-blacklisted-by-visa/) and also drew parallels to the realities of the "social credit score" system used in China (https://news.gab.com/2020/06/26/social-credit-score-is-in-am...). The vagueness of Visa's allegations stood out to me as problematic, given the lack of viable alternatives.
Ultimately, the lack of a provider who acts neutrally is a threat to freedom of speech and expression for all practical intents and purposes.