Definitely no offence taken - I also enjoy trying to get to the bottom of something.
Apologies if I ever come across as dogmatic -- too many years as a lawyer 
Thinking about this some more you must be right that if EV fold = 0 then our EV of flatting would actually have to be negative for this to be worse than folding.
Intuitively it seems really unlikely that we could have a negative EV from flatting a 3b against a range we are ahead of. But theoretically I think that can be the case in certain spots.
If you take the classic case of opening AQ in MP and facing a 3b from BU with a 3bet percentage of 11% from that position, the general advice in this spot is to 4b or fold even though AQ has a 52.5% advantage over an 11% range. (Without going into too much detail the reasons for this - as I understand it - are that we are not going to be able to extract much value from the top end of his range on Ace high boards and when we don't hit we will have to check/fold rather often so that we don't get to showdown often enough against a good, aggressive opponent and therefore we don't get to realise our slight equity advantage.)
This is a rather extreme example of course and it should certainly be easier to play our KK oop. But it's still the case that being out of position means it's going to be hard to stack those hands in his range JJ/QQ/[TT] which we beat since they can check behind on various streets to pot control. On boards with over cards ( to each of those pairs) we also will get stacks in less often. And on boards with Jxx, Qxx, Txx we always end up paying off the sets because we don't plan to get away from a hand often. On Ace high boards, too, we are not going to be able to maximise.
When we face AA, however, we always end up paying off in full since on boards without Axx we basically plan to ch/c down.
I am basically too lazy to do any maths to backup my assertions
but I think we may find it's closer than expected. Against a decent opponent we may find that we extract very little value when we are ahead because they know our range for flatting a decent sized 3 bet out of position is super strong
and they can always fold if we start putting money into the pot, whereas we end up bluff catching against AA all the time and we can't really ever fold our hand. And just to clarify, if we are in position in this spot I think it makes a really huge difference and then I am a lot happier to call.