In TES, Lycanthropes don't actually need to eat people, for the most part. They merely feel a nearly uncontrollable urge to hunt and kill.
"Perhaps it is because they are doomed that makes lycanthropes so aggressive. I have removed the contents of a werewolf's stomach and found more remnants of roots and berries than animal flesh. My conclusion is that they do not need to attack and devour humans to survive. Yet, for some reason they do. Does lycanthropy drive them mad, or do lycanthropes feel the need to spread the disease as a form of procreation?" - "On Lycanthropy" Daggerfall
Sure. They may eat berries here and there but they STILL attack humans. The author did not not know the reason for their violence as he clearly stated. But I think they failed to see the supernatural aspect of it. Kill for Hircine. I think most people that are Lycanthropes in the ES knows this. They have a savage tie to Hircine.
The lore regarding Man-Beast is a little sketchy. I have read alternative sources regarding The Elder Scrolls Sanies Lupinus and they have stated that Werebeast do need to feast on flesh to survive and then there is Bloodmoon were you lost health over time if you failed to hunt. I am of the opinion that Werebeast don't need to kill every night or fullmoon, whatever the cycle may be, but that they would eventually die if they refused to acquiesce to their beastial nature. Hircine doesn't seem of the disposition to allow his victims or 'children' as it were to live their lives and not contribute to The Hunt. Kill or die. Both Bloodmoon and "On Lycanthropy" support this theory. The Lycanthrope the narrator in the book is refering to may have chosen not to be a raving monster and only kills sparingly for survival, the roots and berries being consumed in human form. There are however, other books and snippets of information on Man-Beast that would contradict my theory in places but there you go.
Both Daggerfall and Bloodmoon had the player lose health if they did not kill at least one person. We just can't ignore gameplay elements here. I think it would be a disadvantage to most and one of those cons. And I would agree with what you said on Hircine. Kill or die. Since he is known for being Father of Man-beasts and Sacrifice of Mortals(Yes, somewhere mentioned that he is known by this as well), I think mortals are the only sacrifice Hircine see's acceptable. It is no wonder why the sacrifice of an innocent had happen. In Daggerfall, the player had to kill an infected boy. While in Bloodmoon, he/she had to kill a innocent nord woman who was also infected with the player's curse. Werewolves hunting and killing is serving Hircine's aspects of both sacrifice and...well..hunting.
Some people may think that Hircine does not have much involvment with werewolves aside from the Bloodmoon Ritual. But even before that, he shows concern for his "children". I guess like most werewolves or werecreatures, the infected person does not see it as a gift but rather a curse. Even if he kills one or two people, and Hircine gives him additional powers like in Bloodmoon, they are still self-conscious about being killers. And Hircine finds that unnaceptable. Either cure Lycanthropy and renounce it(With a sacrifice required) or hunt down and kill your prey no matter who or what she is; Man, mer, beast-folk. I don't think he likes someone living in misery while being a werewolf. Cause that's a mockery in and of itself.
"If you would not mind doing a small favor for me, I can put in your possession a most excellent reward, Hircine's Ring. I have a child, apparently miserable with all the blessings I have given him, who needs ... what is the euphemism? To be taught a lesson? A very serious lesson. Does this sound like an agreeable contract, (Brother/Sister)? Ah, good. This child of mine is a wereboar who has made his den in a place called (dungeon). You should have no trouble finding it. After you have put him out of his obvious misery, which should not take more than (time limit) days, go to a place called (building) in (town) and look for a person named (worshipper's name). If you arrive there within (time limit) days from now with the wereboar dead, (he/she) will give you Hircine's Ring."-Hircine.
EDIT: http://www.uesp.net/wiki/Battlespire:The_Requisite_Book_of_Daedra
"Hircine, whose sphere is the Hunt, the Sport of Daedras, the Greatest Game, the
Chase and Sacrifice of Mortals"
There you go.