First, per section 3.3.15 of the WSFS Constitution, Fan Writer (like Best Editor) is an award for the person. It is not, like Best Novel, an award for a particular work. It is thus perfectly acceptable to say "fan writer X is a jerk" and use that as a critique of their nomination.
Actually, it is entirely within the rules to vote based on any criterion, if you want to be a stickler for the rules. Or, people who insist on following the letter of the law do not get to lecture me on the spirit of things.
Second, David Freer is a poor writer, at least with regards to his blog. His posts are lengthy, poorly-thought-out, (see, for example, his 1500 word post on Hugo probabilities, discussed and linked to by me here) and not to me particularly entertaining.
Third, in general the Hugo nominees are asking me and the other voters for a favor. They are asking that we take time out of our day, consider their material, and in the end give one of them an award. I don't know how things work on Planet Puppy, but here on Earth, if one is asking somebody for a favor, normally the person requesting the favor attempts normal human politeness.
For those newly-arrived immigrants from Planet Puppy (and welcome, we are a nation of immigrants!) let me elaborate. Politeness means one does not accuse people of being in a secret cabal. Politeness means that one does not accuse people of voting for works (as opposed to people) because of political checklists as opposed to actually liking work. Politeness means one does not accuse people of "whisper campaigns" and when they point out the non-existence of same call them liars. Politeness (paging Mr. John C. Wright and Mr. Freer) means one does not call people "little girls" or feminine forms of their name or "trying logic with a toddler."
This does not mean one has to agree with me. It does mean that one should attempt to disagree with out being disagreeable. Now, I am a human, with all the foibles thereof, so undoubtedly I have violated this rule. Some may think that this post is an example of me violating that rule and so be it.
In any event, like umpires everywhere, I "call'em as I see'em." To me, "Fan Writer" means "writer who is appreciated by fans" and this fan does not appreciate Dave Freer.