Going through divorce. What is considered good reason to keep child from opposite parent. In terms of other problem step child?

I am sorry to tell you that Wisconsin is a hard state to keep another parent from ever getting visitation. I have experience with this unfortuately. The most you can ever hope for is supervised vistation, and even at that it will be months or a year or so.
My favorate example is a appeal case where they allowed a father that molesed his young daughter to have huber to provide day care for that same child.

Your best chances are if you get child services and the court appointed GAL on the case early. For it has to be in the best interest of the child in Wisconsin. Hire a good family law attorney from your area, and they will know what to do. But be prepared for less than you hope for.