1. The Hugo Awards are being given to fantasy works much too often.
2. You don't see many fantasy works nominated -- the Hugos are dominated by science fiction.
3. The Hugo Awards are much too elitist and snobby. You shouldn't have to pay $40 to vote.
4. The Hugo Awards are much too populist. They'll let anyone with $40 vote.
5. You have to lobby The Committee by casting "write-in" votes to make Them add the categories and nominees you want.
6. The Secret Masters of Fandom control the results, so it's hopeless to get Them to try and change anything.
7. It's terrible that not enough members of Worldcon are voting.
8. I'm a member of Worldcon, but I'm not eligible to vote because I haven't read enough.
9. It's a terrible shame that [Category] has the Same Old Usual Suspects again. They need to nominate someone new to shake things up.
10. It's a travesty, I tell you, that [Person] was nominated for [Category]! S/he is nowhere near [qualified in some way/fannish/professional] enough for it!
Yes, I exaggerate somewhat, but that's this gist of many of the arguments.
And I probably could say this every single year.
Edit, 11:35: Added a couple more points, and thanks to Cheryl for suggesting them.
Edit, 13:05: Added two more thanks to dsmoen's suggestion.