Why are Republicans so against Milliken? I mean, I guess he might be too moderate for some of you, but why vote for a Democrat then?
Milliken was (and is) pro-choice and supports gay marriage. Fitzgerald apparently was more of a conservative Democrat. I feel exactly the same way as you do. Although I am pro-life and oppose gay marriage, I probably would have been more of a moderate Republican at that time, and even if Fitzgerald was closer to my views (at least on social issues), I would still have probably voted for Milliken. Plus, Milliken fought for civil rights.
This, in a large sense, is also why I would likely have supported John Anderson or George H. W. Bush over Reagan in the 1980 GOP primaries (although that's not an entirely fair comparison since Bush I is pro-life, or at least was during his presidency.)