Hi,
I take your point that anecdotal evidence does build up but we humans have a tendency to see what we want to see. The majority are uncomfortable with the idea of fluid sexuality and they can explain away anecdotal evidence.
For example, you mention the behaviour of Roman emperors to illustrate the propensity of most males to indulge in sex with both males and females.
Some may say that Roman emperors are hardly representative of the general population of Ancient Rome or of any society. They had very nearly absolute power, based on their control of the Roman Legions, and while the first Roman Emperor, Augustus, was at great pains to pacify the Senate, subsequent emperors often ignored any check on their power, hence their dis-inhibited behaviour. Even the "wise" ones like Augustus, Marcus Aurelius, Trajan or Hadrian could do more or less what they liked, perhaps not because there was such tolerance of male-male sex in Ancient Rome, but because they had so much power that they became easily "bored" with "normal" sexual outlets and were free to experiment and indulge in more and more "outrageous" acts.
Others may say that a lot of what we know of Roman Emperors' private lives is simply political gossip, designed to manipulate their image to favour the incumbent at the time that the history was written. So a lot of the juicy stories, such as those about Caesar and king Nicomedes, and Caesar and Augustus were designed to harm their reputations.
That is why I think that clever research is necessary, controlling for as many of the variables as possible. If the results of this research refute the idea of males being widely capable and willing to have sex with other men, society permitting, I would not hesitate to accept the result, provided that the research is solid. But I strongly suspect that the opposite is true, as you do.
Regarding my "encounters" they happen in the usual places, typical for the UK, saunas, bath houses, outdoor cruising areas, department store changing rooms (once in the US, in Boston, Ma ;-) from ads on Craiglist, etc. so not really representative but still, a sample.
Cheers,
Schwep