Correct.
All true thieves and assassins know that it's better to work alone.
Can't trust a partner.
My Thief doesn't even trust himself... why doesnt THAT break my stealth?

Nah seriously, I don't care about companions, but at least in Oblivion you could play all qeusts solo. This is not the case with Skyrim.
My Nord is mostly a warrior who does some sneaking and it is annoying when a follower rushes ahead into battle and alerts the opposition, pushes my character who's sneaking and gets in the way of my attacks. I prefer to not use followers and I hate quests that require you to have them.
Well I have avoided too many qeusts (including main storyline). I would like to them on my thief characters, but was hoping for a good mod fix to solve this issue. We shouldn't hate doing qeusts just because Beth decided it would be funny to frustrate stealth players LOL xD