Needle Exchanges are Responsible, Prudent, and Compassionate
No responsible person wants to encourage drug abuse. No fiscally prudent person wants to waste money simply to satisfy a sense of righteous indignation. No compassionate person wants to consign people unnecessarily to death or a living hell. Fortunately, providing injecting drug users with access to sterile syringes allows us to be responsible, prudent, and compassionate—admirable criteria for good public policy.

Needle exchange is the next best thing to rehab.
If we can't get the drug user to rehab.The compassionate thing to do is keep them alive and healthy with needle exchange .
Distilled to it's most basic form, your argument is:
If we can't get the drug user to rehab, the compassionate thing to do is steal money from other people and use it to buy the drug user fresh needles. I disagree.
I am not against helping drug addicts, but this is not an appropriate function for government . This, and nearly every other societal problem, would be handled better and more efficiently through private charity. If you believe so passionately that needle exchanges are the "compassionate thing to do," then perhaps you should demonstrate your personal compassion and responsibility by raising the money to fund one, or at the minimum donate your time to help operate one.