Moglen is not attacking a straw man, he is stating his honest, if misguided, beliefs.
You could now attack a point completely unrelated or only superficially related to his rants about gay marriage and that would be a straw man. You could also, however, argue for or against his points with your own argument.
This is true. Additionally, one could point out the good things about gay marriage. That's a perfectly reasonable approach.
Specific to the Moglen argument, it doesn't make a lot of sense for me to argue against his points because I agree with a lot of them. However, I think the benefits are more important and I won't sit still and let only one side of the argument be presented.
How would you suggest I should present benefits of social networking without you calling me a troll or saying my argument is a strawman?