Ship of the Dark

[Thinlómien]

In Tal-Elmar, one of the unfinished tales in Peoples of Middle-Earth (HoME XII), Hazad, a middle-earthian man, tells his son Tal-Elmar about Númenóreans' dark ships. He says:

In greater numbers they [Númenóreans] come then: two ships or more together, stuffed with men and not goods, and ever one of the accursed ships hath black wings. For that is the Ship of the Dark, and in it they bear away evil booty, captives packed like beasts, the fairest women and children, or young men unblemished, and that is their end. Some say they are eaten for meat; and others that they are slain with torment on the black stones in worship of the Dark. Both maybe are true.

Now, what were these dark ships? Were these just a legend of the wild middle-earthian men or a rumour that had no real basis?

Or did the Númenóreans really "kidnap" some of the wild men? If yes, why?

In my opinion they probably did, since "there's no smoke without fire" and I don't think some wild men would have just fabricated the story. But surely they didn't eat them or sacrifice them, that was most probably superstition and fear from the wildmen's side that caused such rumours. But what did they do with them then? Did Númenóreans have slaves? If yes, then I think they were taken as slaves. But shouldn't this all be against the Númenóreans' high sense of morale? I admit they thought they were lords of everything and "better" than the middle-earthians, but still...

Can we actually compare Númenóreans with European colonialists?

Any thoughts on this?