This is true. It's a heuristic our brain uses so it doesn't have to reevaluate things every single time we experience them. Whether or not this is good or bad is very debatable and depends on the context.

The heuristic is something we evolved through evolution to help us make choices quickly and survive better. For example we know to just trust whatever the group leader says when there is danger rather than having an open debate every time he speaks because that could get us killed.

In the case of HN, does it matter if we have to fully evaluate the content every time before we vote (w/o knowing who wrote it)? I don't know. I think there are probably cases on HN where that heuristic is still to our benefit. I don't think theres black or white here, the costs on both sides just need to be weighed...

Also I think everyone should realize there is a small parallel with the ad hominem attck which is DH1 from PG's post about how to disagree with people (http://www.paulgraham.com/disagree.html). In this case it's exactly the opposite, vote up because of who it is instead of based on the merit, as opposed to vote down (or attack) based on who it is as instead of based on merit.

...which is detrimental. They won't if we don't let them.

Actually, most the time it's not detrimental. As the post above mentions, it's a very useful heuristic.