I think that anytime you really limit the people who can volunteer, you have to ask yourself if you are keeping out someone who would be awesome and beneficial, and if you are setting up some kind of "safeguard" that is a true one or a false one. Does it give you a false sense of security that the leader is a dad? Why? Are there no dads who have been pedophiles? Of course we want to protect our children from predators, and those who seek positions (professional or volunteer) with our young people need to be checked out, vetted, and perhaps have criminal background checks. That's cumbersome but some people feel it's necessary. Keeping out gays is ridiculous - gays are no more likely to be pedophiles than heterosexuals. In fact, the Boy Scouts are actually responding to public pressure to stop discrimination because so many people are pulling their kids out of scouting and not supporting any fundraisers.
Having a dad involved is great - great for the son, great for the dad. That's one kid who at least gets to activities on time! LOL. And it teaches kids that stepping up to volunteer is so important. But people should volunteer where their talents are. That dad might be much better as the church choir director or the classroom newsletter writer than as the scout leader.
Meanwhile there are many terrific volunteers and former Scouts who believe in it and have so much to offer. They have organizational skills, team building skills, creativity in helping to design merit badge projects, community contacts, camping skills, and more. It's essential that we show our young people that it's important to be involved in your community whether or not you have a child that age - "it takes a village" and all that. Being a dad doesn't automatically give you abilities, compassion, leadership skills, or even a pass that says "I'm safe around kids."
And what about the kids who don't have a dad? Why should they feel that they can't have an important person in their life to serve as troop leader? It's also (sometimes) hard for the parent troop leader (or soccer coach or Sunday school teacher...) to be objective sometimes. There may be favoritism or the appearance of it, sometimes a particular dad may be much harder on his own kid. So it's all about the individual.
So, yes, we want our kids to be safe - but we have to be honest about being able to "tell" if someone is a nice person or an abuser. Their credentials as dad (or as we know from the news, as priest or as counselor or as teacher or as youth worker) don't, by themselves, indicate the risk or absence of risk.