Don't know if you've got kids or not. I have, and in your scenario the thought that when they are older they could pop out to a corner shop, buy some bread, milk and a big bag of heroin, fills me with unimaginable terror.
Why? I mean yeah currently heroin is currently seen as an extremely dangerous drug. But really that's just it's street form. When dealers "cut" heroin they cut it with agents that can cause diseases and such, but if it were legalized and regulated they would be getting "clean" heroin which is much safer then even morphine which is used around the world in hospitals today. Even in the UK they prescribe Diamorphine which is heroin without the brand name.
So yeah I get that it would be scary but really the only "danger" is becoming addicted and since it would be available at any corner shop it would be much easier to get.
Just saying... your worries are misguided.