Franken is a serial sexual harasser and perhaps even serial sexual assaulter (groping counts, doesn't it?). This is not the case of him saying something once or acting inappropriately once--it is a pattern of behavior that he is not denying although he has underplayed what is clearly something quite systemic in his own character. He does not belong in the Senate, he should not be representing people nor should he be paid by taxpayers with public funds. Everything he does now is tainted. The Democratic Party needs to have some core values and treating women decently should be one of them. Franken may have done good things for women in general, but he has bad for the individual women he has encountered. Franken leaving or getting kicked out is the right thing to do.
It is also, conveniently, good politics. Not just that the Governor of Minnesota will appoint a Democrat so it does not affect the balance of political control of the Senate in the short term (that someone has to run in 2018 to replace Franken could be dicey). It is good politics because the Democrats are increasingly becoming the party of consistent values and the GOP is the party of opportunism. This ain't bad optics going forward. More importantly, it is good politics because women are more than half of the electorate, and the gender gap already favors the Dems and will favor them more so. Sure, more than a few women have other interests/identities that cause them to vote against their interests as women---they may be rich, they may love their guns, they may be racist, or whatever.* Still, alienating some women by being the party of sexual assault is not going to help the GOP, and by drawing a clear line between the Democrats and the Republicans on this, the Democrats will benefit. The GOP can suppress the vote of minorities and the young via #voterfraudfraud voter id laws, but how can they suppress the female vote? I am sure they will find a way, but it is much harder.
* Yeah, I am still bitter about white women voting for Trump, which upset my prediction last fall and gave us this darkest timeline.Anyhow, I will get over the heartbreak of having a guy I have long favored turn out to be sleazy and hurtful to those who was supposed to be helping. Will the GOP get over being the party that preferred a child molester in the Senate and an admitted sexual assaulter in the White House? I am not so sure.