IMO, chips on their shoulders the size of Kentucky because they refuse to forgive others [who do not ask to be forgiven]. They also are afraid to admit [or think seriously about] their own sins, because they are selfish [and bogged down with the muck]. And hence, they are lonely as well, and disparaging of a faith that forgives sins (through Jesus), which is evident on its good peoples.
It has been my experience over the years that there are about 1000 excuses for people leaving the Catholic Church. The first is poor catechesis, the second is un confessed sin. If it is the second you can tell quite easily based on what they rant against during discussions.
The other thing I noticed is that they want to drag others out to justify their own "decision." It is the "See I must be right since so many are following me" attitude.