You can chew coca for a long lifetime to little or no ill effect; millions have, ever since the Spanish broke the nobles' monopoly on the leaf---and I guess you can use crack for a lifetime, but it doesn't sound like it would be as long or as net-pleasant as one I'd want, even were it legal. Similarly, I'd rather need my pipe of opium nightly to fall asleep and relieve the aches and stresses of the day than need to inject morphine or heroin in order to function at all.
I'm all for advancing our knowledge and abilities, but when we start using chemicals that have not stood the test of time, we're in greater danger than before. This is not limited to synthetic chemicals: some of the non-THC components of pot's seem to ameliorating effect in those individuals---and they do exist---for whom THC can be a contributing factor in the development of clinical schizophrenia...but the drugs laws have helped to shift the profile strongly toward THC. Tobacco was used by American Indians, but never constantly, and usually in combination with other plants that at least reduced the total nicotine intake (even as they might increase tars, for all I know).
Again, we should not limit ourselves to those things our ancestors developed, but we should maintain an healthy scepticism toward the untried, especially when we're hacking with our core wetware.
"The one charm of marriage is that it makes a life of deception a neccessity." - Oscar Wilde