VISA........
(a) Visa is a business. They are entitled to accept or reject any clients they wish. They are also a monopoly.
(b) I can't "blend" with the idea of bestiality sites, child porn, rape, torture sites. However, each country has their own laws on this and they differ - and they are entitled to make their own "rules".
If VISA have taken upon themselves some form of censorship, this is bad. Next week *anything* can be censored irrespective of whether this is legal or not in the country where VISA do business. It may be, depending on the country and their laws, that there is a legal arguement for "restrictive trade practices".
If what VISA are doing is selecting the companies they wish to deal with on the basis of content, there is an arguement that this is not censorship, but simply a choice they are entitled to make.
This is, in a way, is similar to ticket sales where there are considerable problems - VISA has a free choice to deal with ticket sales companies or not.
The main problem is that VISA is a monopoly operating globally and controlling the majority of the card market. This is unhealthy for both consumers and merchants. No one organization needs to hold this power. If that situation existed within one country, such as the US, there would be FTC intervention as happened with the US media recently.
Either way.. there is a no win here - either trade with VISA or not
