an addiction requires a physical component.

If this is your definition of addiction, a "mental addiction" cannot exist. I am happy to concede I am wrong and improve my knowledge if you would be so kind to point me to sources prooving this is the general accepted definition of the word.

Masturbation and porn use doesn't fall into that model at all; the consequences of not masturbating is that you don't feel something pleasant, not that things start hurting.

Well – no. Not for all people. While "blue balls" are a myth, bad mood, emotional instability and even aching genitals are at least for some people consequences of sex withdrawal. Craving does exist as well.

It's simply not in the same category as alcoholism, or addiction to nicotine, opiates, etc.

That's true.

If you speak to a psychologist that is trained in and specializes in sexual disorders--again, not one that's using a religious/spiritual approach, but one that's evidence-based--you are unlikely to find anyone that regards it as a legitimate disorder

Well — actually I haven't met any psychotherapist who doubts that there are people with non-substance related addictions. I have no experience with sexual addiction myself – only met a couple of patients who claimed to have overcome it – but I did work with patients with eating disorders, which we viewed and treated as addiction, and with pathological gambling, which is viewed as an addiction as well.

Ok – so far to the existence of "mental addiction".

Regarding "porn addiction", I agree, that a habit has to meet the criteria for addiction. So I agree someone isn't addicted to masturbation/porn

unless you're doing things like masturbating at your desk at work 3-4 times/day, or needing to pull your car over on the way to work to compulsively masturbate.