Businesses should not be boycotted (by conservatives) based on the groups they choose to market their products to. As the author says, it is the job of businesses to sell their products.
However, it is entirely appropriate to hold businesses responsible for the donations they choose to make and the causes they support through their policies, such as gay marriage, etc.
I think the circulation of the gay magazines involved is so low that any payment for advertising is nothing more than a hidden contribution to their social and political agenda.