Less valid transactions in my mempool will make my node unreliable in predicting the next block and estimate fees, especially in extreme cases where it could be critical. Not relaying is the same as not running that node for those transactions, does't stop anyone else. The filtering node slows down it's own to verify blocks - will be later to reach the tip, will waste hashrate in that time if mining. Only the fastest route counts so even a supermajority would not be signficant.