Why does Bishop Thomas Tobin want to deny Communion to Rep. Patrick Kennedy?

Tobin argues that the reason why Kennedy shouldn't receive Communion is because of his pro-choice stance on the abortion issue. OK, so Catholic bishops give Communion to Mafiosi and child molesters and other offenders all the time, but for some reason, they only take issue with pro-choice Catholic politicians. How is abortion or supporting a woman's right to choose any more sinful than ually victimizing someone or bumping off someone who's already been born? Since the Bible specifically forbids murdering those who have already been born, one would think that the bishops would at least throw out the Mafiosi.