I relayed the statement of a Republican that I witnessed with my own eyes, and it's just another datum in a big pile that includes your own statements on the subject. Is your assertion of symmetry, that there's a similarly large ideologically-motivated boycott of Hillary Clinton on the horizon, backed up by similar direct evidence?

I have to doubt that, and assume you're projecting, because the rationale is not symmetrical. Extreme Republicans will boycott McCain on ideological grounds, while Clinton's negatives have more to do with her personality, style, and political tactics (and I, personally, am finding her attacks on Obama to be more and more distasteful--her negatives are growing with me, too).

The asymmetry is broader than just two candidates, just this year. The Democratic side has never placed much value on developing an ideological monoculture--spirited philosophical disagreements are part of the Democratic landscape, and aren't interpreted as crimes against the Party. Being a Democratic politician necessarily means being a coalition-builder, and uniting the Party is all in a day's work.

Historically, I think the closest the Democrats have come to an ideological boycott was in 1968 over Lyndon Johnson and the Vietnam War. Johnson resigned and the party rallied behind Humphrey; it's hard to say how it would've gone in an alternate timeline in which Johnson didn't resign, but quite possibly there would've been such a rebellion.

Conventional wisdom has it that a big factor in GHW Bush's failure to be reelected in 1992 was his violation of the read-my-lips promise, and a boycott by Republicans. I'm hard pressed to think of another example based solely on ideological differences. Possibly going down the foodchain, to governorships and other local races, might reveal other examples.