I see your point, brash_stryker. I don't mind that Anakin's turn was a conscious decision. Vader himself in the OT was a pretty calculated villain, who wasn't constantly "drunk" on the Dark Side whenever he killed anyone.
That said, I agree with you that there isn't a good sense of Anakin being turned. I don't think the problem is his motivations though: it's because he already is a pretty dark character at the start of ROTS: he already has a case of genocide below the belt, and just let himself being goaded into killing an unarmed man. After he has turned to the Dark Side, he does the same things: comitting genocide (the Jedi) and killing unarmed people (the kids and the Separatists).
I think this can be helped if we "nicen" Anakin up, starting back in AOTC: cut him talking back at Obi-Wan in the elevator and in Padme's apartmant, cut him arguing with Padme in front of the Queen, add the scenes with Padme's family (Anakin at his nicest here, I think), tone down his creepiness around Padme, imply, but don't show the Tusken slaughter and cut the following confession.
Same goes for ROTS: cut down his whiny and brooding moments (what little there is) before the turn, and take out every display of emotion after the turn, such as him crying on Mustafar.
If we are going to make Anakin's distrust of the Jedi a big factor in his turn, here's my suggestion: after Mace sends Anakin away to inform Palpatine that Obi-Wan has engaged Grievous, let him overhear the following conversation between the Jedi about the possibility of having to force Palpatine from office and taking over the Senate. If I'm right, you can even see Mace looking over, to see if Anakin has left yet. It could fit perfectly. I'm sure there is some blue scene footage of Anakin on the ROTS DVD that we could use.
Anakin overhearing this conversation could work nicely with the earlier scene with him and Palpatine at the opera house, when Anakin confesses the Jedi don't trust Palpatine, and Palpatine accuses them of being against democracy and the Senate. It would also be nicely paid off in the turning scene where Mace as Palpatine at saberpoint and Palpatine says "I told you the Jedi were taking over".