Here is an article by George Weigel in Newsweek that gives a pretty reasoned argument as to why "most" Catholics are finding it very difficult to vote for Senator Obama, and why those who are so ardently supporting him should seriously think again.
I am quoting a bit of it here to make the point:
"To suggest—as some Catholics do—that Senator [Barack] Obama is this year's 'real' pro-life candidate requires a peculiar kind of self-hypnosis, or moral confusion, or worse. To portray the 2008 Democratic Party presidential ticket as the preferred 'pro-life' option is to subvert what the word 'pro-life' means."
Why? Because the public record amply demonstrates that Senator Obama is not the abortion moderate of our professors' imagination, but a genuine abortion radical. In the third presidential debate, Obama described Roev. Wade, the 1973 Supreme Court decision that obliterated the abortion law of all fifty states, as "rightly decided"—a judgment with which Professors Cafardi, Kaveny, and Kmiec have all disagreed in the past. Moreover, Senator Obama's defense of Roe extends far beyond anyone's "elegant theorizing." Support for Roe was Obama's stated reason for opposing Illinois bills aimed at providing legal protection for children who survived an abortion.
You may read the rest on your own. We aren't single issue candidates by any means, but this one issue is a very serious one and we can't in good conscience vote for someone who is so ardently on the side of those who would sacrifice the life of the most defenseless.