Blindsiding an alliance every time they go on the offensive is surely not a worthwhile precedent to maintain for the sake of this game's meta and overall health. Unless you would rather force every sphere into shells, waiting for the other to make a move, stagnating in perpetuity or crushing them with a sucker punch when they finally strike.
As an alternative, spheres could join together and make coalitions so large that it could not be opposed by any counter attack, and then you might actually have reason to fear being next on the chopping block. Neither of these are options I think anyone would enjoy.
Also Rose is hardly "everyone else" lol