I don't think he was complaining about the terminology but in terminating a life that was worth living.
Perhaps it was debatable then, but certainly not now. I have just seen too many smiling faces on the downs kids to think their lives aren't worthwhile. Even back then, the testimony in the court revealed they were very loved by their mothers and Klugman's DA revealed he loved his downs brother very much.Which is, of course, highly debatable ... and that episode incorporates such a debate, with the Prestons on opposite sides.