I really don't care who supports AFA or who they support, and I don't care who WalMart supports when it has no impact on me. Giving an organization a commission from sales generated through that groups website is a common internet business practice. As long as the organization does not violate the terms of service of the company providing the affiliate commission, I don't have any problem.
And that's for you. Others, such as those who support the AFA, see doing business with a gay organization as something that affects the culture of our nation, and that affects others. As Paul said to the Corinthian church, bad company corrupts good morals. Of course we might disagree as to what denotes bad character...