The first part is a criticism of his music. That's fine, it's an opinion.
However, to argue that he's trying to 'cash in' is an unfair accusation unless you have some damn evidence or something. He's been pretty vocal about his support for LGBT rights. And of course Tegan and Sara have been rallying for longer. They've had a decent following for much longer. Macklemore didn't have any success until 2012. "Same Love" isn't even his most successful single (nor the first for the album).
An don't argue that it's disrespectful to us in the LGBT community. You don't speak for us at all. At least Macklemore is using his position of influence to talk about these things, instead of making unwarranted claims on a message forum.
I think something like this is a step towards.....progress for LGBT rights and advocacy. Yeah Macklemore maybe using his position of power and influence to gain some new fans...but I think it's at least a step forward.