The only evidence we have of Anakin not being able to go back to get his mother is the Jedi way. As he tells Padme on the cruiser, "Attachment is forbidden. Possession is forbidden."
That's the whole problem with him. Had Anakin been taken when he was a baby, he wouldn't be attached to his Mother, just as Obi-Wan and Mace aren't. They don't know them. Anakin was raised by his mother. She was the only thing he knew. She's the one who guided him to be this selfless individual at nine in Episode I. That doesn't just turn off just because you're going to be studying the Jedi Way. This is why Yoda didn't want this...."He's way too old."
As for his turn, the Darkside does play a part but I'll even admit that it's way too subtle in that sequence we he kneels before Palpatine. It's implied.