"Alas, the church is full of sinners."
The Church is a hospital for sick souls. One would expect to find sinners there! Its where we belong. :)
"Which is why Paul was pleased with the Bereans for checking out what he said by comparing it with Scripture."
You don't think the Bereans were reading +Mark do you?
They could have been. Nothing says that they weren't. If Mark was written in the 40s, they well may have been. They were reading whatever they had. Their Scripture was no more inspired than ours. The principle applies.