Thing is he was a nice guy and a good scout master. I found out about this a while ago, while it was still under investigation, and honesty we were shocked. This is one of the reasons my Son quit scouts. First it was this guy (and he is not the only one) then BSA dropped the ban on gay scouts. My Son, who loved Scouts and was well on his way to Eagle, decided enough is enough and asked if he could be done with scouts.
Read a book on stories of experienced cops a while ago. The gist of the cops who handle predators is just as you pointed out. These predators make up their mind at a very early age that they like young ones. They will build their entire careers around their sick desires to end up in a place of authority over their victims, coaches, priests, teachers, youth ministers, etc. They are very patient and will build their "web" with social camouflage (i.e. married with kids) and look like pillars of society on the surface.
The one thing I remember from one cop is that they often are seen as "cool" and "hip". They will have the latest gadgets (X-Box, sports cars, ski-dos, etc.) and often seem like saviors to single moms with "troubled" kids. It is all part of the web. The cop also said that almost every time these predators get arrested, there will be many people around him who will say it is not true, they can't believe it, etc.
I point this out so that others will be on the look out for the "cool" coach, not the hard line drill sergeant type and the "hip" youth pastor, not the boring pious one.