You're crazy if you think he sacrificed his career. The majority of people support Stem Cell research.
In the not too distant past, there were good Germans who supported.....uh he who must not be named.
Point is, majority does not equal right
Frist is a "Republican".
To seek any political office as a "Republican" you go first through the Republican Primary not the general electorate. So the public's majority opinion is meaningless. Even more so, it was an issue in the last election and was NOT a primary issue. Nor will it be in '08. Bush won standing against it and Reeve's widow.
The Republican activists that vote in primaries have a large contingent of 'social conservatives'. While not all are against ESCR, the majority are.
Frist has practically no support as it from conservatives. Conservatives see him, generally, as a blank uncharismatic slate that cannot control his Senate the way Delay controls the House.
Up to this point because he is Senate majority leader, people have held their tongues (mostly). Frist has now just aliented fiscal, smaller government and social conservatives with this stance, the last being the main wall protecting his back. All for their own reasoning, in opposition. He has been praised by Reid, Bozer, kennedy, Arlen etc.. the MSM outlets. All repulsive to conservatives.
His politocal career doesn't end just because of this, but it is the final nail.