They need to make it that you can be rated down but your post can still be seen if its sub-default.
The point of the karma system was specifically to allow for idiocy to be weeded out of the conversation, so that it didn't get derailed.
That mattered a lot more in the past, when the boards were much more active. Now it would only really matter for the XIV board, where it doesn't matter anyway, because the XIV board is the second level of ****.
Realistically, the problem is that the XI community on these boards is atrocious. Well, it was always elitist, with the game being what it was, but the individual job forums were usually pretty helpful (the warrior board, for instance, taking steps to get new Warriors level-appropriate GAxes).
But as the game aged, the newbies disappeared and people quit. So you really just ended up with a bunch of elitist idiots on a board padding their own and each other's inflated senses of self worth. When FFXIV's forums were created, a lot of them started posting there, too (for unsurprising reasons). That pretty instantly established the culture of the board as a FFXI 2.0 board, and it's not likely to change.
Let me put it this way - when FFXIV came out, a lot of posters on Zam's non-FFXIV board were playing it. We all just used a different thread in the general games forum to talk about the game, rather than gouge our eyes out with the XIV board.
TL;DR: If you don't have a thick skin, don't use the FFXIV board. Or the Asylum. Though the Asylum is a lot more inviting...