Unfortunately that's not enough for many people. I think the main problem is having the right spirit, of no compromises, of seeking perfect purity and love of God. It should be simple, but modernism gets people by its many intricacies. It sure sounds like a good idea to go to the traditional mass and be in union with the Pope of the Catholic church. Put it that way, and there's no need for anything like the SSPX, right? WRONG!!!
It's also an issue of ignorance. They don't have any doubt, or at least no positive doubt, though the danger exists. I would think learning about this issue would strengthen a person's faith.
I wonder how far little pamphlets of a list of positive doubts would go