The risk here is that the rocket explodes and spreads the stuff far and wide.
It wouldn't be nice if in an human exploration on outer space we find a container full of unknown harmful waste from another civilization. That shouldn't be our first option.
Not to mention the really bad problem if a rocket carrying the waste exploded. You've basically made the problem 10,000x worse.
> It wouldn't be nice if in an human exploration on outer space we find a container full of unknown harmful waste from another civilization.
The unshielded fusion reactor which we orbit around is likely to be a bigger problem.
There is a chance that it will fly back to earth. Not to mention there is also the risk of explosion during the launch. And also it’s not scaleable and super expensive.
The Mariana Trench is better: 10 km of water then it's a subduction area so it'll end in the Earth mantle.