But chlorine is also a poison and it actually affects your health very positively: it kills waterborne diseases while not affecting humans at all.

(https://en.wikipedia.org/wiki/Water_chlorination)

I can see the case for ethanol also having no long-term effects. Though it is in much larger quantities than chlorine and does have short-term effects, so this is some evidence against it having long-term effects.

I actually agree with you that alcohol is probably bad, but I think the reasoning "of course adding poison to your body is unhealthy" is not correct.