Campaigns are built to fool us into thinking that we're voting for individuals. We learn about the candidate's family, her job, her background -- even her dog. But we're primarily voting for parties. The parties have just learned we're more likely to vote for them if they disguise themselves as individuals. And American politics would work better if we understood that.
I always feel irrationally guilty as I go down the list marking the D candidates and only the D candidates. But at the end of the day, that D represents a list of policy priorities that I sympathize with far more than the priorities of the R. So there's no real reason I should care overly much about the name in front of the letter.