Originally Posted by MuzzleVelocity

I dont think its as cut and dry as "upon unverified assumptions concerning the behavior of others - incorrect". If the OP or anyone else on a MUP wants to pass a family of 4, regardless of hills or oncoming traffic, there is no possible way to know for sure that one of those wobbly kids won't veer right in front of you just as your passing. Just like when driving on two lane blacktop you have no way of knowing if the oncoming car at 60 MPH won't have a blowout and veer right into you. What can you do to 100% avoid such "faulty" assumptions? Stay home and be an agoraphobic?

All I'm saying is that it is just about impossible to do anything in life without *some* assumption of the expected behavior of others.

If the golden rule is "pass when safe to do", I think the OP made a judgment call that based on his line of sight, and based on what he reasonably expected the speed of oncoming traffic on a crowded day to be, he decided that it was indeed safe to pass. When his reasonable assumption was proven incorrect, he took action to be safe and merged back into the right lane.

You can't fault the OP unless you are trying to say that he deliberately decided "its not safe to pass this family, but I'm gonna go for it anyway".