That's interesting. I suppose the exact role of dopamine in male sexual function is poorly understood.Anyway as a personal anecdote:
I don't suffer from ED but I did notice that I "last longer" when having smoked. Not sure if that has much to do with the canna or is more a state of mind thing.
You mention how some strains aren't really suited to sex, but don't seem to consider that there are strains that would do the opposite?I think ED is more diet/exercise related. If you have a bad diet and do not exercise you are much more likely to have these kind of issues. Cannabinoids may promote better sex although the actual smoking part decreases blood flow which will inhibit a healthy libido. Overall i think if you eat healthier and exercise regularly, you can avoid ED. For me, smoking before is nice, but like mentioned above, some strains don't work as well and can make one too distracted/not in the "primal" head-space.