Probably the stupidest phrase you'll ever hear. It's like saying the war on murder, rape, or all crime is lost, so we should have laissez-faire attitude relating to those problems too. The fact is there are tens of millions of drug addicts in America and many more that are affected by the collateral damage drugs cause. I'm not an absolutist. The approach of just letting people do as they please is not applicable in this case. If anything we need to ramp up our efforts to combat drug use.
And how would you suggest we go about "ramping up" the existing folly which the existing drug laws are? Based on what already has been done to stop those who are inclined to use drugs from using them it should be clear to the reasoning mind that any effective means of ensuring abstinence would involve the most brutally totalitarian methods imaginable -- such as are presently in use in the Philippines and includes on-the-spot execution.
Now that we've seen that force doesn't work it seems reasonable to try intensified public education, which is the means by which use of the most addictive drug of all, nicotine, was reduced by almost 80% without arresting anyone.
As for those who insist on self-destruction via abuse of powerful narcotics, there is no way within the social boundaries of a free society to prevent them from doing it.