zvei dinim,
First of all your mashal is not accurate (because even the “second candy” here is not akin to cyanide). Second of all, yes that would be muttar; unadvisable but muttar.
I understand that tobacco is a carcinogen and therefore any amount can cause cancer. However if the amount of the carcinogen is very small, the odds of it causing cancer are miniscule. I can’t access the full version of that study so I can’t look at the numbers, but is occasional smoking more dangerous than driving or getting X-rays?