Honest question
These are good points, but you don't have to advertise. You can do it in secret purely for revenge beyond the grave, so you can die with a little smirk on your face.
Life is going to be pretty cheap in a collapse situation, perhaps including the value of your own life.
Right, the above analysis assumes we're approaching this rationally. The truth, of course, is tons of people seem to enjoy pettiness and would get satisfaction of the thought that who killed them ended up dying themselves. Whatever, I'll let them enjoy their revenge fantasies about death and dying while I stay alive.
Well, just be careful whose food you eat.
There's nothing irrational about ones own life becoming so miserable and difficult that you cease to put much value in it. The way some people whine about the burden of their own existence, it would seem to be irrational for them to continue living - yet strangely they do.
That only works if the bandits know that you did this. So you'd need to advertise your partially poisoned stockpile to everyone in the community. Advertising your stockpile is a very bad idea and will attract tons of attention, so you shouldn't do this.
So let's imagine you don't advertise your stockpile and just keep quiet. But if they just come in a shoot you, the poison doesn't do you any good since they kill you and didn't know it was poisoned.
If they take you alive and you tell them that it is poisoned or they see a warning sign by your stockpile, now they know they need to torture you until you tell them which ones are which. They probably won't trust you at this point and will go Pulp Fiction medieval on your ass. Make sure your stockpile also includes abundant amounts of lube and prepare for the big gay.
In conclusion, you need guns or you're going to get yourself killed--or worse.