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Re:Facebook reveals its cryptocurrency Libra by desdiv on Tuesday June 18, 2019 @11:14PM (#20220518)
You are correct if you interpret "Visa and Mastercard" as literally Mastercard Incorporated and Visa Inc.

He used "Visa and Mastercard" as a metonymy for the entire payment processing network i.e. payment gateway + issuing bank + acquiring bank + card networks. The total fee for the entire network is indeed 3-4%, and as you rightly pointed out, Mastercard Incorporated and Visa Inc. fees actually only make up for less than half of the total transaction fees.

Re:Facebook reveals its cryptocurrency Libra by thedaveoflife on Wednesday June 19, 2019 @02:09PM (#20225605)
Of course the are not "taking" it either... they are issuing credit, allowing ease of purchase and providing fraud protection