Since you asked for a list of why anyone would support obama over keyes... I obviously have not one reason, but if you are actually wondering what Alan has done that is so polarizing, or what he could do to improve his standing amongst conservatives or republicans, or how his candidacy might be in any way damaging, here it is.
Alan would do better if he was perceived as obeying that commandment you just mentioned. Lots of bitterness against him on this forum and nationwide, is foundationed on unrepentant and terse statements he has made about our President, and in general, my party's leadership. If and when this race is over, his attitude towards attacking and blaming its leadership will surely become more apparent than it is now.
what statements?
To the contrary he helped Bush to the election in 2000 by derailing McCain in the debates (read the transcripts). Moreover, over the entire campaign he has supported Bush at every opportunity even though he disagrees with some of his policies and tactics. Keyes is no Buchanan. In fact Keyes support for Bush in 2000, I am convinced, diminished Buchanan's impact in that election. We should be thankful to Keyes that we do not live under the reign of Gore.