A fork is not an attack. It is a fork. Bitcoin does not care about forks, because they are not Bitcoin.
It IS 100% an attack when the hardforkers are trying to steal the Bitcoin brand.
There may be some "friendly-forks" that just want to hardfork BTC to issue their altcoin and they recognize themselves as an altcoin.
Another very different story is when government shills like Jeff Garzik or Roger Ver try to turn segwit2x or BCash into BTC, claiming it's the real bitcoin. In fact, Jeff Garzik claims in november exchanges will list segwit2xCoin as BTC and it will become de-facto Bitcoin (of course they are bribing miners and merchants with fiat gov-sponsored money). These are the terrorists against Bitcoin that need to be flushed.