I think most TBM females refuse to believe that JS had sex-capades -- they euphemize the liasons as "marriages," which somehow makes it OK. Some of them insist that the "marriages" didn't include physical contact. A third rationalization is that God commanded him to do it, so it's OK and there are some things we just don't understand but it doesn't matter b/cuz they're not important to our salvation anyway. When confronted with quotes from the women involved, they will shut down the discussion and walk away in a huff, or they will argue that it's Satan trying to tear down the church, quotes were taken out of context, etc. (This part is usually followed by accusations of apostasy and trying to wreck their testimonies. Then they walk away in a huff).
Personally, I believe that it has more to do with being afraid of what it would mean if they DIDN'T give Joeseph "behold my flaming sword" Smith a free pass.
I mean, can you imagine what it would mean if they openly admitted that Joe "hold my rod" Smith abused his power to have sex with women (including 14 year old girls and married women), and then likely had his friend perform abortions? They might have to take a moral stand on other issues too! Like blacks and the priesthood, women and the priesthood, the roles of women in the church, the lies told by the prophets (including Gordon "Build" Hinkley and Tommy "The Widow Maker" Monson)...
It's much easier to shutdown at the first sign of morally questionable conduct... saves you from having to ask the hard questions and make difficult decisions that could effect your personal and social life.
It's not that he gets a free pass, maybe the TBM just don't know his real history.
Many women, and men for that matter, do not know all the details of JS's escapades. I'm a convert to the church and all I knew was the image of happy and eternally married Joseph and Emma. Even when I asked I was told he got the revelation but it started with BY. As far as I remember, there was nothing taught in manuals or classes about JS and polygamy. When I first learned he had other wives I was disturbed but was still not easy to de-program myself. At church we are told how great he was and how his enemies and the enemies of the church try to twist the facts of his life. I'm a convert and I had a hard time with my 'testimony' of JS yet it was still hard to believe all I read about his infidelities. I can only imagine how it is for those who have been born in the covenant.