The blowjob scene...

No. Believe it or not, sometimes guys have difficulty achieving erection in certain situations.

Tully was just released from prison after a 15 year stretch. During that time he's had absolutely no contact with women, and probably no sexual contact whatsoever in prison. He's with a strange women who he just met, in a strange situation, and all of a sudden without any buildup, flirtation, or sexual energy between him & Doreen he finds her eager mouth wrapped around his cock.

In society men are generally viewed as these sex crazy creatures who can go from 0-60 in 3 milliseconds flat, and who are down to shag whenever, wherever, and whoever. But this is not always the case. The ability to achieve an erection is strongly linked to your mental state, and Tully was probably overwhelmed with lots of different emotions in that scene. To begin with he was probably feeling anxious, uncomfortable, and probably a little intimidated by her forwardness, and this quickly turned to feelings of shame and emasculation as he found himself unable to get hard in her mouth.

You've probably heard of erectile dysfunction before, but probably don't know that the vast majority of men experiencing ED can trace it to psychological issues and severe mental blocks, rather than physical problems. Drugs and alcohol are also a common cause, perhaps you've heard of "whiskey dick". Men generally feel shame when this happens, the partner often blames herself and or takes it as a sign he is not attracted to her anymore, and for many men the anxiety surrounding the "idea" of being unable to achieve erection and disappointing their partner leads directly to them being unable to do exactly that. It's like a self-fulfilling prophecy.

Sorry for the long explanation but I hope that helps explain things. Just because a man fails to achieve an erection doesn't mean he is gay! It happens to most guys at some point in their lives. For me, it has happened before after a long night of drinking and drugs, and it is quite embarrassing if your partner is not very educated or understanding.

I believe that scene was meant to show his commitment to the white supremacy cause. He says something to the effect of denying one's self trivial pleasures when it comes to a goal.

By him denying her after 15 years in prison shows us two things:
1) How committed he was and,
2) How those above him had close to absolute control over him. He is brainwashed to believe that the cause is worthy when we know he's just a pawn to further their gain...whatever they want that to be.