I wouldn't put coke and heroin in the same category exactly. Of course, as you say, people experience it differently. Coke is a slippery slope but not as bad. The thing about coke is, is that it is immediately short term addictive. Not necessarily with the first line, but after the second or third of the night you start wanting the next sooner and sooner, the need becomes stronger and stronger. Of course, a good night's sleep, once you finally go down, will remove the effect. I would say this, people who think of it as a "miracle drug" might very well be in a high risk category of becoming addicted. I remember my first time, I thought it was cool, but nothing that great. Crack is worse, the first hit is addictive, again short term, nothing a good nights sleep won't cure. But people who do these things fall prey to habituation and eventually real addiction. I never liked the uncomfortable twitchiness of stimulants, so I put it down easily.
Heroin I've never actually tried. It's too rich for my blood, and I was also afraid I'd like it too much. Stimulants aren't for me, but depressants are another matter. It's a physical addiction that can kill you if you just stop once you've gone far enough. The effects, from what I understand, are such that when first beginning, a little will do you for longer. You don't need much and it lasts awhile. The amounts become greater and greater as you go. The long-term addiction is much sooner.
Alcohol is another slippery slope. Some people can drink responsibly and not fall prey to alcoholism, but others become increasingly dependent. The real dangers of alcoholism are the long term alcoholics. I used to drink profusely. It was fun, it loosens you up, makes you more social, etc... It has many good side effects. But, I began to notice, not so much in myself but those around me, that the booze was starting to get on top of them. They began to need it. My sister would lecture me about smoking pot and addictive personalities and such, meanwhile, she gets shitfaced drunk every day of her life. My father was an alcoholic. He would get off work and go right to the bar. Drink til he was incoherent, go home, sleep, wake up, go to work, rinse, lather, repeat. He tended to stay off the sauce on the weekends, and he was able to go for a week or two at a time without drinking if the need arose, but in the end it killed him. I have an older friend, pushing 50, who is a serious alcoholic. He can't go a day without getting seriously drunk. He gets cycles of hangovers. Booze to cure it, which just makes it worse the next day. He tries to clean up every now and again, but I've never seen him go more than a couple of days before he starts rationalizing that he has to drink or his body will just shut down. I've seen him cry about friends that have died from kidney failure and the like. His sister-in-law was so bad they put her in the hospital because she wasn't doing anything but drinking, she wouldn't even eat. Get this, a ketchup packet or two every now and again was her lunch. A friend of his blew his brains out, bad divorce, but booze pushed him to it. I could go on and on. It's disgusting.
In the end, I quit because I like to be in control of my actions. Drugs like these take control. Some sooner, some later. Now if I could just quit smoking. But the thing about smoking is that it doesn't steal your mind, just your will. And the anti-smoking commercials nowadays make me sick in their raw blatant propagandism. Whiners and complainers bitching that they didn't know it was bad. The tobacco companies owe them something. Weaklings. I think it should be obvious that inhaling burning smoke into your lungs is not good for you. And the surgeon general's report has been out a long time. If you don't know smoking is bad for you, then you're a retard.