Yes, Visa and Mastercard make money with adult internet and yes, it's only a small piece of their overall revenue.
On the other hand... even if you're a millionaire, you do care about 200 bucks.
Again, yes, there probably is more money in "keeping certain people happy".
But..adult internet isn't only bad pornographers and unsatisfied customers who charge back.
It's also the customers who are satisfied and love what they get and are willing to pay for it.
If Visa bans adult, they will pay for porn with their Mastercard ( if they don't onw one, it's possible that they will get one ).
If Mastercard bans porn, they will pay with Visa.
And those who pay with their Visa ( or Mastercard ) for porn, pay also for other things online with it...
And if f.e only Visa bans porn and then when even only 5% of porn surfers who will have to chose between Visa or Mastarcard, will chose the second one, and will use it in everyday transactions, that's again lost revenue for Visa.....
Bothe Visa and Mastercard care about marketshare...
Just my thoughts...
