I agree with the other posters on 'someone asked me about.... so I had to research.'
I'm a history buff so I will have that up my sleeve for later, comparing old literature with 'new light'.
Personally I took a different tack. I had not long been affiliiated with this website and other enlightening material so I wasnt ready to tackle the lies, false doctrines etc.
But I very truthfully told my Mum when she asked about my inactivity that I had to leave due to crippling depression brought on by the massive burden of meetings, field circus, study, being treated like crap by so called friends, heaped with lots of guilt for not doing enough and fear of armaggeddon for my kids, hubby and myself. I told her of the huge weight lifting off my shoulders, my depression improving over 90% and the fact that a loving god would never want me to feel the way I did in the org. She actually accepted this explanation without getting defensive but of course had to let me know that armaggedon was just around the corner and god expects us to make sacrifices for him. I was happy with the outcome of this and didnt look like an apostate.
If anyone expresses concerns for my spirituality I tell them its never been better. I have actually not picked up a bible willingly and read scriptures ever in my life until now.
So you can always tell them that mental illness... even if you lie about it...is caused by the org's slavery.