Yeah some cocaine is less pure than others but pretty much anything you buy on the streets isn’t going to be completely pure. Even if the people you buy from are legit the people they buy from might not be, even the producers do dodgy shit. Do you seriously trust everyone in the chain from here to Columbia? There are websites online where you can see the results of lab testing from drugs sent in from various different countries. I would read one of those and disillusion yourself.
It’s also definitely not as safe as you make out even if it was pure. You’re kidding yourself if you think it is.