I can't finish the Companion quest line because I don't want to be a Werewolf.

I can't finish the Theif's Guild and Assassian Guild quest lines because I don't want to be a total jerk.

That leaves just the Mage's Guild...for my non-magic using warrior character.

Poor design, IMHO.

You can cure your werewolf curse at the end.

lol

been there before

Are you on the PC? because there are mods for the Companions. You can say NO to the WW life and the story continues. Same with the thieves Guild. You don't need to be a Nocturnal agent. Not sure about the Brotherhood... I usually destroy them.

You can finish the Companion Quest line and not be a werewolf. In fact it is sort of .. interesting when you have to fight yourself.

The only one with poor design is the Companion's. Lycanthropy should not have been part of a major questline, because most people I think don't want to be a werewolf for most of their characters, but the Companion's are the Fighter's Guild of Skyrim, so warriors who don't want to be werewolves get nothing. Sure, you can just cure yourself, but if you roleplay it might be against your character to become one in the first place and one way or another you have to deal with guard's talking about your ear fur forever .

You can complete them, you just choose for character reasons not to complete them.