It's not that lethal for everyone. Junkies inject and snort it. I suppose they have developed a tolerance, perhaps due to prior heroin use.
Fentanyl is sold on the street. I'm sure it is cut with something, but it is sold as fentanyl. Some junkies seek it out and prefer it to heroin.
You left out the part of my comment that mentioned they develop a tolerance, asshole.