Hydrogen sulfide is highly toxic (it's comparable to carbon monoxide). I doubt anyone in their right mind would put it intentionally in a place where it could leak around humans.
But it can occur naturally in natural gas.
But it can occur naturally in natural gas.
It's a bad comparison since CO doesn't smell, which is what makes it dangerous, while H2S is detected by our sense of smell at concentrations much lower than the toxic dose (in fact, its biggest dangers comes from the fact that at dangerous concentration it doesn't even smell anything due to our receptors being saturated).
It's not what's being put in natural gas, but it wouldn't be that dangerous if we did.