This feature has previously been requested and rejected for mathematical/technical reasons. The short version is that matchmaking wouldn't just be checking your list, but ten full blacklists; any positives mean that entire match has to be rejected. The simple explanation is that implementing such a solution is not easily solvable.
If you are so inclined, the problem boils down to what is known as a P=NP Problem, and mathematicians have been trying to solve that for decades. Until they do, matchmaking blacklists of this sort in any game (not just League of Legends) are not technologically feasible.