Hacker News Reader

On that note, how much neo-nazi propaganda would I have to watch in order for advertisers to avoid me?

They never would. Unless somebody decided to make public that they were advertising to neo-nazis. Only then do they have to go into damage control.

Why is this? Is it because it is easier to categorize users as opposed to content, or do ads perform better when targeted to specific audiences? If I had to guess I'd think that audience targeted adverts would perform better, but here we have a large amount of companies upset that their adverts are appearing next to specific content.

you're wrong, advertising targeting factors both these things.

I'm aware that it's possible to buy ads both based on content in placements rather than audience based targeting, but the latter is much more pervasive on digital and the former typically requires larger budgets and know how that your average advertiser doesn't possess.