I understand your position and other people's about investments and similar issues. However, the difference is that Frist's investment in HCA is HUGE; HCA is a major provider of abortions, including late-term abortions; Frist's history on abortion is conflicting (he has said that he is "personally pro-life but" thinks abortion should remain legal, then flipped and said he was pro-life except rape, incest, life of mother.)
Putting the issue of his financial stake in the abortion industry for a moment, Frist has waffled on abortion issues. He is described as a "moderate" by the press (not that I believe everything the press says), and I question his conservative credentials. I do believe that it's important to have a pro-life conservative as leader of the Senate. I don't think Frist is the man for the job.