Harm reduction to me is no harm being caused
So you don’t actually understand what ‘harm reduction’ means despite using the term. Got it.
In any case, this is an argument over the validity of a method, which is not what the meme is about. The meme isn't saying "Don't argue with other leftists when your positions clash!", it's saying "Remember that there is broad room for cooperation and allyship, and that a different kind of leftist is not automatically your enemy just because they have different end-goals."