* This might be obvious, I'm not sure. But: Moby-Dick, while he's most likely just a big whale and not a malevolent force, is still badass and unstoppable, and most characters are aware that going after him is suicide even though they kill huge whales for a living constantly. The fact that he's a WHITE whale may explain this: in nature, albino animals are much easier to see and therefore usually eaten very quickly as babies. Moby would have been a swimming target and had to defend himself every day to an insane degree, sort of like a boy named Sue. If Moby-Dick grew up constantly threatened by predators he would HAVE to be the ass-kickingest whale around or he would have been munched on by some shark or shanked by some whaler as a baby whale. So no wonder he has no problem sinking whaling ships- he's the most experienced fighter in the whale world!
** Except that in the book Moby Dick isn't albino. He just looks white because he's covered in so many scars. And only the upper part of his head is actually white, so he's probably referred to as the white whale because that's normally all sailors would see of him.
*** Well, he ''is'' directly referred to as an albino ("And of all these things the Albino whale was the symbol. Wonder ye then at the fiery hunt?") but even without that, he is clearly not just white due to scar tissue:
"But even stripped of these supernatural surmisings, there was enough in the earthly make and incontestable character of the monster to strike the imagination with unwonted power. For, it was not so much his uncommon bulk that so much distinguished him from other sperm whales, but, as was elsewhere thrown out—a peculiar snow-white wrinkled forehead, and a high, pyramidical white hump. These were his prominent features; the tokens whereby, even in the limitless, uncharted seas, he revealed his identity, at a long distance, to those who knew him.
The rest of his body was so streaked, and spotted, and marbled with the same shrouded hue, that, in the end, he had gained his distinctive appellation of the White Whale; a name, indeed, literally justified by his vivid aspect, when seen gliding at high noon through a dark blue sea, leaving a milky-way wake of creamy foam, all spangled with golden gleamings."
Obviously, he's ''mostly'' white even if he's not a true albino (the whale that inspired him, Mocha Dick, apparently ''was '' an albino, though)... So the point still stands.
* Sperm whales are very aggressive creatures. They have been known to attack ships without being provoked. Moby Dick isn't attacking ships because he is being hunted, he is attacking ships because he is what he is.