In case you haven't been following what has been going on. The NY Times published a tabloidesque hit piece on Assange, and has failed to defend Wikileaks on the basis of journalistic freedom.
It's pretty clear that the Times management consists of war hawks who oppose Wikileaks b/c of their neoconservative political beliefs and desire to please those with political power.
Think about when the last time the NY Times published any remotely controversial investigative journalism... oh yeah it was the articles that supported the claims that Saddam had WMDs.
Strangely, the Times (a good but ardently neoconservative) paper still manages to fool progressives into thinking that it offers a sympathetic voice. Sadly the pressures of competing in the online world have left the paper with no choice but to sell off its journalistic integrity year after year.
If anything, one would hope that a paper like the Times would have taken a skeptical but journalistically sharp look at the leaked info and would have held off on the ad hominem attack on the Wikileaks founder, at least until some evidence was offered in support of the allegations against him.
And no, I don't think the total buffoonery written by Krugman, Dowd, and Herbert counts for any progressiveness points. If anything the three are a sideshow act with no relevance to the issues that matter.
What if there are more people who think that than message board sentiment analysis would lead you to believe?
What if the New York Times simply doesn't agree with your take --- ok, the popular take on places like HN --- about Wikileaks?
These are the questions that matter: Is WikiLeaks a journalistic entity? Why or why not? Is it OK for a bank/financial entity to block donations to any entity, journalism or not? *If money is speech (http://en.wikipedia.org/wiki/Buckley_v._Valeo) how is blocking donations not a criminal offence?
"I do not agree with what you have to say, but I'll defend to the death your right to say it." - Voltaire
And, of course, since money is speech, it's fully within your rights to donate to wikileaks (cash, check, wire transfer, money order), just as its within Visa's rights not to accept Wikileaks as a customer.
EDIT: And just to be clear, I'm not trying to argue that there are no political motivations behind the decisions of Visa and Mastercard. I'm just answering the question about why this isn't for some reason illegal.