Not all victims of molestors are girls, many are boys.
If you wish to call a Shmiras Halashon if a known molestor attends your shul with your nieces and nephews (Or any other relatives), go right ahead. I will protect my family first and if it means I did an averiah, I will take that averiah. Better I take such an averiah than anyone become a victim
And people who cheat in their taxes (I dont mean take an illegal deduction, I mean serious cheating like not paying sales taxes or paying employees in cash) are likely to be dishonest elsewhere as well