A lot of people would not be able to scrape the money together for private care, and be left to die slowly at home, with no NHS to ease their pain or perhaps give them the chance to overcome their affliction.
If your mother/father/sister/brother/spouse/close friend were diagnosed with lung cancer, after a lifetime of smoking, would you applaud a decision to deny them treatment?
The honest answer, again, is no.
One of my friends is always enraged by these things, he often starts ranting about Georgy Best drinking away his liver and then continuing to drink when he got a new one. I think treatment should be given if it's not at the cost of others. If it's things like transplants where one is unrepentant and will happily destroy their body again and one is likely to look after themselves then it's more beneficial to give to the latter patient.
If it's not a priority treatment and not a great drain then treatment should be given in some cases (possibly make them go private and pay for it in others).