That's a useful distinction for a doctor to make, especially if they are treating an addiction with medication. But in the broader sense, a chemical substance addiction shares many similarities, with respect to psychological compulsion to do something, with a purely psychological compulsion and both are, broadly, "addictions" in the common non-specialized sense that most people use it.
Truthfully the only people who become addicts carry an addiction gene. This is the reason why most adults can drink alcohol, yet around 10% become alcoholics. The same goes for marijuana, and even porn. If you don't carry the genes for addiction you will not become an addict. You can become dependent on drugs, but once you get off them, your not going to go back.
I think that 10% become problem alcoholics but I suspect technical alcoholism rates are higher than that. My family has had several functioning alcoholics who had a compulsion to drink every day but were never violent or abusive and could hold jobs and so forth. I'm aware that it's genetic, which is why I don't drink alcohol and never have. I don't want to know the hard way whether I'd be an alcoholic or a bad one. It also may be why I can feel the mild addiction to chocolate as a compulsion because I may be susceptable to addictions. Maybe you don't have those feelings but others do. Perhaps someday we'll be able to sort out the people who can't handle certain things from the people who can. Right now, we can't. And if you are susceptable to addiction, what is harmless experimentation to someone else can create a spiral of destruction that ruins your life.
For example Rush Limbaugh, he took basically an opiate (thats what most prescription pain killers are) but could stop after he detoxed and he isn't going back. An addict can't just stop, even if you got all the drugs out of his system he'll be driven to go back. The only way for an addict to stay clean is to completely stop taking anything that gives them a high.
And, as any alcoholic will tell you, avoid being exposed to the temptation of your addiction because the memory of how it felt to take the substance nver totally goes away. A single drink can bring back an alcoholic's alcoholism. A single pill could get Rush Limbaugh addicted to pain killers again.
And just as food compulsions are difficult to overcome because one must eat food to live, sexual addictions are also difficult to overcome because sex and the sex drive is an integral part of most normal lives. And images designed to create a sexual response in the viewers have become very mainstream, which is what many conservatives mean by the "pornification" of the culture. It's difficult to avoid sexual images even if you want to. Even if they are not "porn", per se, they could lead someone back down that path.
I know alot of Christians think addicts are just weak willed sinners but its just not the case. They are still responsible for their actions however.
People must be held responsible for their own actions, even if they can't help themselves. That's one of the things that can help a person fight a compulsion, too. That's something a lot of liberals have trouble grasping. Letting people evade responsibility because of compulsions only makes their problems worse.
But that still doesn't mean it's not useful to help people avoid those things that will drive many to compulsion because the cost in destroyed lives, no matter who is ultimately at fault, is very high. And Bob Crane didn't only wreck his own life. He damaged the lives of two wives, several children, and others he came in contact with. That's why such compulsions are important to others. Their negative effects often don't confine themselves to the person with the compulsion.