Again, you’re citing your own assessment of your own experience as evidence, and furthermore you’re generalizing it to everyone without any foundation for doing so. It is not evidence; it’s an opinion or judgment. Suppose I had exactly the opposite experience with masturbation as you did? Or suppose I have an allergy to a particular food - should I warn that no one should eat it, based on my own experience?
If you have the opposite experience, then our conflicting accounts would need to be weighed up against each other - and probably the evidence of more practitioners gained to see where the consensus lies.
Regarding alcohol, as you note, medical authority warns against alcohol abuse; it doesn’t condemn drinking absolutely, the way the church does with masturbation. Furthermore, the harm caused by alcohol abuse has been well-documented by objective, published studies - far different from anecdotal evidence and self-observation.
Yes, but coming from an authority such as the AMA you realise that the conclusion is based on MUCH MUCH observation both by professionals and by alcoholics self-reporting their own experiences. The evidence of that one alcoholic simply adds to the collection of evidence the AMA already has.
Same with Church teaching - it is NOT simply plucked out of thin air, it is also based on observation and knowledge - much observation and knowledge - of the practical and psychological (not to mention spiritual) harms our sins, including the sin of masturbation do to us.
And you wouldn’t take one example to the contrary against the weight of AMA evidence - neither should you against Church teaching.
Example - I have a great-great grandma who lived to 107 and smoked right to the end. I wouldn’t take HER word, albeit truthful, that smoking did HER no harm as evidence that smoking is OK. Not ever.
Or ever say that it wasn’t a sin, even for those like her who seem to be unharmed. If she knew the usual consequences and did it anyway, it most likely was at least a venial sin. She was just blessed that God spared her from the usual ills smokers suffer. His merciful sparing of such doesn’t make her smoking morally fine and dandy (no misuse of any drug, tobacco included, is).
Similarly, the fact that God may have spared you from at least some of the consequences and ill-effects of masturbation doesn’t mean it’s not a sin for you.
Most things taken to excess are harmful; that doesn’t make them immoral by themselves.
Masturbation is itself the excess, though - it is the natural sexual instinct taken ‘to excess’, or at least abused and misused. God has taught us very clearly what sex is for - in scripture and outside of it. That is the unity of married couples and the procreation of children. Anything outside that is already an ‘excess’, just like any killing outside of self-defence or defence of country or other legitimate exceptions is already an ‘excess’.
There’s no such thing as ‘moderate’ masturbation any more than there’s ‘moderate’ murder.