It's pretty clear that they're talking about web sites that host and or distribute material to which they do not own the rights.
At least it is to me.
I have just reproduced your copyrighted work and DU is hosting and distributing that reproduction.
No, it's not a Lady Gaga song or a movie but the same laws apply. DU was recently sued (and thankfully won) by Righthaven for copyright infringement because someone had posted a small snippet of one of their copyrighted news articles. I have, in fact, infringed on your copyright
more than the poster did by posting that snippet. If all of this sounds nonsensical, it is. But that does not make protections under U.S. law any less strict or the legal avenues any more constricted.
Under the partnership that this OP describes, could Rigthhaven have asked Mastercard to deny the process of financial transactions for Democratic Underground until the court case was resolved?
Absolutely.That's the problem and an attempt at hopefully defining the ambiguous nature of copyrighted material and especially the danger of credit card companies who are willing to extra-judicially prevent credit card transactions based on copyright infringement.
PB