See?
so instead of showing us in that side quest the fact Dorian didn't do his duty to continue his family line and have some kids we are shown his dad tried blood magic to change Dorian's gay-ness. This is just stupid plot line.
Instead they could have focused on Dorian not getting married and having children as the core of the plot.
This is so wrong that I can only assume you are doing it deliberately. The issue is laid out plainly as Dorian didn't want to go through with the marriage. His father attributed this to him being gay, not Dorian, his father. I realize that people think everyone should just be all butterflies and rainbows about being gay, but as we can see from responses in this and other threads where this comes up, this just isn't the case. I suspect that your whole issue to Dorian's quest is that Dorian is gay, not that it comes up in the quest, but just because that's how he's written.
As a heterosexual male, that had max "approval" with Dorian, I can tell you, I didn't come away from his quest feeling the same way you did. I interpreted the information as it was presented, w/out a preconceived bias about him being gay. I knew he was, but it didn't bother me, and I really think he did hit on me, I'm just not sure, because even if he had, I would have deflected it away and gone on about my business, much as one or two of my female friends have in the past: I love ya' Rob, but I'm just not that into you. No harm, no foul, one doesn't know where something can go until one pursues it. Sort of akin to all the flirts in DA 2 for Aveline, that were fun to take, but weren't going to get you anywhere.
I came away from Dorian's quest feeling like the core issue was that Dorian refused to marry the girl and have future Magister babies. I don't think being gay was his root objection, I think he just objected to the policy in general: Why marry someone if you're not going to be happy? Maybe if he'd liked the girl, he could have done it? We don't know, but I came away feeling like his opinion of the girl, and the basic idea of the concept in Tevinter played a bigger part than his being gay.