Great questions, Top. And I've thought alot about the Mac situation, too.
On the one hand, yes Mac is partly to blame for what Dobson did. Did he honestly think that Dobson would simply back down and allow himself to be quietly led away? Did he think that by holstering his gun in response to Dobson's complaint that he was unarmed would earn Brownie Points with Dobson and suddenly he'd be repentent? Or that his actions would somehow earn Dobson's last minute respect - honor amongst thieves, etc.? I couldn't tell if Mac had actually anticipated Dobson coming at him and wrestling it out and Mac actually wanted it, or if he honestly (and niavely) thought that putting his gun away/making himself "equal" with Dobson would somehow spur Dobson to allow himself to be meekly led away in cuffs. I guess I'd have to watch it again to be certain, but if Mac had expected/welcomed the fight, then honestly, shame on him, he should know better; it's not worth losing his badge over certainly, but he should know better.
As far as his reaction to the inquiry, I honestly think it's more initial gut reaction than anything else. For a guy who's always espousing the benefits of going strictly by the evidence and ignoring the emotional, he certainly does go by his gut reactions alot, doesn't he? He does make an honest effort to go strictly by the book/evidence etc., but since the beginning of S1, he has allowed himself to be led by his emotions time and time again. It's partly (IMO) disbelief that anyone who knows him and his record could honestly think him capable of such an action, and he's incensed by it. He knows that despite his culpability in Dobson's fall by holstering his own gun, ultimately he's innocent of pushing Dobson - and he's outraged that anyone, especially his colleagues, would suspect differently. Never mind the fact that Mac went tooth-and-nail after Truby, in Mac's rather one-track mind, *Truby was Dirty, therefore deserved to have people not believe in him/take him down. Mac is Innocent, therefore deserves to have people believe in him/not want to take him down.* He's seeing it too black & white for his own good. I don't think he fancies himself above the law, but in this particular case, I think he fancies himself above investigation, for the simple fact that he knows he's innocent. Guilty of godawful judgement, but innocent of the crime. Making it out as a political backlash makes him feel better. I think just the opposite; let the facts speak for themselves, prove his innocence in the accused crime, and put it to rest for once and for all in the minds of both his colleages and the public. If he doesn't officially get investigated and proven innocent, then there will always be some who suspect a cover-up, or his guilt. I think eventually Mac will come to this realization too, but right now, he's allowing his emotions to rule him, despite himself.
At any rate, great storyline!