I think they should be required.
Because other wise it pretty much would be the same as the current rating system. The whole point of the Reputations system is to give users feedback on how other members think they contribute or dont contribute to the forums and help them improve as members of the community. If somebody just votes "Good" or "Bad" then that wouldnt really give sufficient feedback to help improve yourself so I think it should be required
And on the topic of people abusing the system , That will be un-stoppable and that is a fact. If a user feels he is being abused he can simply send a Private Message to an administrator with a subject like "Reputations Abuse". Also on the form to rate a member it should have a little not like..
*Abuse of this system will result in a ban.
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