I'm also not sure why you keep going back to the opening mail comment, as if to suggest that the crime is stating that it's a big deal for a well meaning parent to open and hide mail from an adult child. The OP's parent was wrong, wrong, wrong, and your being okay with it (while apparently not "defending" it) doesn't make it right, or okay, or understandable.
The fact is, while it sounds like your kid is talented enough to be okay in his upcoming cycle without your kind assistance (notwithstanding your inability to control yourself), and you seem to know which obvious lines not to cross, a lot of the well meaning folks you are defending (who don't understand why they can't call admissions offices, do all the research, open the mail, decide where to apply, write the applications, take the tests, etc. for their budding genius future MDs) are going to destroy whatever chances their kids have in this process when they annoy the adcoms. No amount of being offended or not understanding why is going to change that.
What you seem to fail to understand, while you seemingly yearn to relive some part of your past through your kid, is that your kid (and, likely, the OP as well) would be just fine if you weren't on here and he had to do everything himself in order to research and execute an application cycle. The kids who actually need their parents to do what you are doing are not actually ready to apply to and attend med school, so all of the parents' effort is really, in the end wasted, insofar as it is unnecessary (and possibly self-defeating) for the kid who doesn't need it, and won't work for the kid who does!!!