Ya. This is why I try not to get involved in discussions on whether mod packs, or hell, mods in general, are legal. Maybe they are, maybe they aren't. I don't have the knowledge, or a reason, to really care.It's not stealing if everyone wins.
But in this case, as Ash said, its really about respect. Which IMO, is an opinion. If you just want to play minecraft, which is a perfectly valid position and I don't respect someone any less who takes it, then you don't need to care. I am more in the middle of and have an opinion.
But most of this would probably be solved if at least one of the major mod authors says why he doesn't want his mod in a mod pack. Although I don't blame them if they don't.