I would guess it's more likely that the Slashdot moderation system is too hard to implement. It also requires a lot of finetuning (like how to determine how many moderation points to dole out to users based on their karma and activity). The Hacker News developers seem to prefer to keep things simple, so they might reject Slashdot-style moderation for being too complicated, but that doesn't mean they don't like it in principle.
The source is that the HN mods know about Slashdot, and people have been asking for those features here for 15 years, and they haven't been implemented.