*spoilers*
Please help me understand this - what were they planning on doing with "Andy" once they were done with the procedure? Would they maybe move to a different city or something with their son, provided it was successful, and start afresh?
****SPOILERS****
Somehow, I doubt the procedure would have been successful...
But in the off chance that it worked out, they wouldn't need to re-locate. Remember Jason was home schooled and Maryann was his first friend. So all the outside world new was that the Mr. and Mrs. Young lived in an isolated house with their sick son. If the operation was a success, the only one who would have known that Andy was not the same boy would have been the "meddling" Maryann... So Katherine had good reason, besides being a complete psycho bitch, for wanting to keep the two apart.
*Spoilers*
I see, so you are saying 'he' would probably continue to be home-schooled; I can buy that.
Even I tend to agree that the procedure would not have a high chance for success. Also for some reason, I felt that despite having such meticulous attention for detail, their plan as a whole did not seem completely fleshed-out. Interesting movie though.