Take it as an opportunity to separate ideas from persons. You may agree with an idea even if you dislike the person proposing it (and the other way around, of course).
I'm not sure who this is trying to convince. People who agree with him like me, it probably won't affect much. People who want to invade Syria are the type of people that will see his name and only feel vindicated in their belief. You know Fox News, et al. will spam their viewers with "This is what Putin says, it must be wrong."
I don't know if there is really a lot of people sitting on the fence on this one, other than the apathetic who won't read it anyway.
And he's doing a great job. The offer to get Syria to put their chemical weapons under international control was brilliant. Obama was saying, "They crossed a red line, there's no option but military," and then Putin put forth a peaceful solution.
That the rational thing to do as a reader is to ignore his identity and examine his arguments is mostly irrelevant, since that's not actually what people do. I suspect it's a miscalculation.
Edit: minor changes for clarity