This ban seems unfair, and if it is rooted in an anti-astroturfing policy, then that policy appears way too aggressive - no one wants HN to be a marketing site for mega-corps, but passionately defending one's favorite company shouldn't result in a ban. Also, the moderators have all the power, and accused none. While moderating is likely arduous and maybe even moribund, being a fanboy/AstroTurf-er especially one not behaving badly, isn't worthy of silencing/banning (that's my opinion).
The consumers of HN content have a healthy skepticism towards polarizing opinions, and as with all social media, have their guard up on what can be blindly trusted. This ban assumes your average HN-er cannot tell a fanboy apart from a neutral third party - which is not the case. Let opinions be, let the fanboys talk freely (as long as they're not impolite), and trust the HN audience to use their better judgement in drawing any conclusions. I don't think anyone assumes the top comment on any topic to be an endorsement by YC/HN, or it's users.