At first, it was rather selfish, (and I maintain, its not only proper, but right to do this for yourself): To wit, why promote a religion and way of life that has hurt you for senseless, defenseless reasons?
JW's are always fond of pointing out how bitter those who leave are. How convenient! Of course, this is tantamount to condemning the 9/11 widows for being pissed off because of what happened to their partners. (remember that? there was some backlash)
JW's hurt me, destroyed my marriage, and as an elder and missionary, I got to see how they destroyed other people and families as well. I was almost killed in an overseas country that ships young indoctrinated people overseas in groups of 50 twice a year to spread their poisonous propaganda to the ignorant in ill informed. How could I promote that? How could I stay in it?
I firmly believe that the reason to leave must always be personal, whatever personal reason it is for each individual. Without real damage, unfortunately, people will stay around with a dull sense of pain and a dull questioning of why they are in pain, never realizing that the reason is the cult they belong to.