I think that it's generally a good rule because it acknowledges that for most anime, it's impossible to make an informed judgment on the quality of a series after a single episode. It discourages kneejerk reactions from people who wish for their vote to count (though there will always be attention-whoring MAL reviewers who write reviews for shows after a single episode just to be the first reviewer), but it certainly doesn't compensate for the propensity of MAL members to use the four-point scale and certainly can't counteract bad taste (man, I sound like a snob.)