From my experience, if someone leaves the church because they don't understand the gosple and didn't have a testemony, they don't invest their time and effort in pulling other people out, they go on with their lives and have no axe to grind.
On the other hand, people who leave because their pride is more important to them than the truth, and who did have a testemony that it was true, are driven to rail against the church and pull as many out with them as they can so they can point to the ones they pulled out in a vain attempt to justifiy to themselves what they did. They want validation for their deeds that deep down they know are wrong.
Of course there are exceptions to this....
I was raised Catholic. There were certain questions that were often put off with, "You'll find out in the end." Outside of church my father would teach me beliefs from what he had read in the Bible. When I began to investigate the LDS church I felt I had come home. Everything I had been taught all my life from my father, were the beliefs in the LDS church.
I still have respect for the Catholic church, but know I am where I belong. I have been to other denominations and have always felt uncomfortable. Of course, it was funny that my mother (who is not active in her faith) at first believed I was "going against my beliefs" because I was no longer Catholic. Would it be better for someone to have no religion than for them to be active in the LDS church?
I know I originally had a point, but then went on and on. My original point (somewhere in there) is that even though I am no longer in the Catholic church, it is not my place to bash it.