And yeah, while there are obvious drawbacks to being seen as the baddest mother in time and space, there are definite benefits, too. If he'd done it in "Human Nature," for instance, it would've saved a lot of lives.
Well, perhaps we could see that as a tipping point, or certainly an event that made him start changing the way he did things.
In "Human Nature"/"The Family of Blood," he ran away rather than face the bad guys directly ("You coward!" "Oh yes, sir, every time.") He wanted them to just not be able to find him until they ran out of life, so they would die without him getting his hands dirty. Obviously that backfired pretty spectacularly, and Nurse Redfern guilted him pretty bad over it.
Later, he admitted that what he did to Martha over the course of "The Sound of Drums"/"Last of the Time Lords" pretty much ruined her life, giving her family a year's worth of PTSD in a few minutes and turning Martha into a hardass soldier instead of a Doctor.
So maybe that's when he decided he needed to start being more proactive, taking the fight to the bad guys rather than letting them come to him, taking the hard road himself rather than forcing his companions to do it. Hence the attitude in "Forest of the Dead" where he dares the Vashta Nerada to take him on.
Notice that all the companions he had before this change of heart were the ones who turned into warriors in "The Stolen Earth"/"Journey's End" - exactly what the Doctor didn't want them to do. They shouldn't have to, he should be the one to do that. The companion he had after the change of heart - Donna - didn't fight at all. She was terrified, didn't know what to do. Perhaps the companions reflect on the attitudes of the Doctor at each particular time.
So again, the result is to turn into more of a badass himself, rather than force other people to do it. No more regular companions, because he doesn't want to do to them what he already did to Rose, Martha, Donna, Jack, Sarah Jane etc. Thus at the same time as he's thinking, I've got to be tougher, he's also not got anyone to tell him, no you don't. Hence the Arrogance of the Time Lord arc of the Specials season. He starts to believe his own hype - hey, I
am the baddest mother in time and space, so don't mess. I can do what the hell I want. He turned into exactly what he was trying to stop other people from turning into.
I had hoped that facing an entire race of his own people who'd gone through the same changes, and seeing up front just how bad it was, and deliberately humbling himself in response, we would have got over this. But apparently even a regeneration didn't entirely rid of him of this attitude, as his first act as 11 is to bully an alien race with the force of his fearsome reputation. "Who da man?!"
By the time of "The Pandorica Opens," and his big speech of "Let someone else take the first shot," he's basically just confirming all everyone else's worst fears about him, that he's spent a while now making sure they believe about him.
