Historical sites are normally somewhat maintained and preserved. They are also quite often seen by tourists who are interested in those sites.

Most sunken ships, they just sit there and nobody wants to take responsibility and maintain them so that no oil and fuel gets into the ocean. Furthermore, there is little to see. Sure there is some historical information on them but we should save those otherwise the ocean destroys them (surely but slowly).

If those sunken ships were properly maintained, I would also call those scrapers thieves because they take something that belongs to someone else and it has value to them. But since most are just sitting there, waiting to slowly decay.

The only things those scrapers should be held responsible for, is when they damage a tank or something like that which pollutes the ocean (and there should be resources on how to do that safely). But then again, those fuel tanks will leak at some point anyway (they won't last forever) and it should be our responsibility (as humans) to make sure that does not happen.