there's no social contract/consensus that exchange should not vote, the problem is only how exchange should communicate with their users on this issue.
from committee perspective, the problem is how to define the rule to prevent one big account from controlling the whole network, maybe one option is to restrict the committee number one account can at most vote.
no proff to tell that exchanges are more likely to abuse power, they do not spend capital for the stake, but they are responsible for their users.