Coffee in regular amounts, nicotine not by burning, a beer or two now and then... shouldn't be controversial. Less obvious but still true: opiates at maintanance levels under supervision, regular amphetamine in moderate dosages, MDMA or ketamine on occasion. Loads of drugs in loads of usage scenarios really are "safe".

But just because supervised heroin won't kill you doesn't mean it's somehow good, actually. That's a separate judgement.

There's surely no upside. It's overwhelmingly likely to make you less healthy and less happy. But so will too much bacon and sitting.

Chairs are still safe though, by any sane definition.