Under IFR the collision avoidance job is legally assumed by ATC for all aircraft filed and flying under IFR. If an IFR aircraft is in visual conditions, it must clear itself from other aircraft flying under VFR, but any aircraft filed under IFR is separated from any other IFR aircraft by ATC. Of course, in cloud in controlled airspace, this means that you are fully protected, but might only be threatened by some wacko who has not filed IFR.