It seems this thread is lousy with misconceptions. Maybe I can clear some of them up.
Firstly, bisexuality is only the ability to interface with both men and women on a romantic or sexual level.
Attached to bisexuality are no other characteristics, such as high libido, or the inability to sustain a monogamous relationship. Similarly, gay men are not all rapists, nor all child molesters, nor all promiscuous (as is still assumed by much of the the US, and even more of the world).
Bis are among the most discriminated against, of all the sexual subsects. Not only do phobic hets regard them as gay-by-default, but unthinking (or at least ignorant) gays regard them as traitors-to-the-cause, ergo, few bis will reveal themselves to questionable company. In parts of the San Francisco lesbian community, Bi is regarded as a perjorative epithet, hence many lesbians play with boys sometimes, but are never bi.
Similarly, though, het males in US culture (let alone anywhere else in the world) are often so afraid of being even slightly gay that many are in complete denial of their own homoerotic interests (something akin to the gay panic [http://en.wikipedia.org/wiki/One-drop_rule] (The propositioning gay is outing the straight to himself). The stigma of homosexuality is severe enough that it could easily account for many (if not all) of the proclamations on this thread of pure, absolute hetero-normativity, argued ad baculum.
(Considering the modal [http://en.wikipedia.org/wiki/Mode_(statistics)] demographic of The Escapist, I would expect a large portion of us to be precoital and most of those that remain, new enough to sex and attraction to not be fully familiar with their full gamut of paraphilias. Juxtapose to what actually appears in the thread.)
Bis do not easily fit into a single category. Some bis have only dated women, some only men, some have had plenty of lovers of one sex, only one (or a couple) of the other. Some have had an even mix of partners. Some go through boy phases and girl phases. Some are attracted to both all the time. Some are intrinsically monogamous (or at least serial monogamists, breaking each relationship before considering the next). Some are casual sex [http://en.wikipedia.org/wiki/Polyamory] (or casual sex with one, yet committed sex with the other). Some are not sexually active at all.
(As a side note, while dispelling myths, monogamy is considered normal in the 20th century and the contemporary era. But it is atypical of humankind at large. While premarital or extramarital affairs have been considered abbherent throughout Europe during the middle ages--thank the Church for that one--this hardly stopped everyone from bedding their neighbors, and their neighbors' wives, and their neighbors' daughters, and their neighbor's lifestock.? And in plenty of classical eras, including the old-testament biblical times, men were allowed to have and share concubines, as well as their wives--that's plural, as in polygyny--although women were expected to be chaste to a single man, yet often were not, opportunities willing. And many classical European cultures seasoned their year with holidays in which sexual restrictions were lifted, and anyone could boff anyone they wanted. Consent was frequently optional, at that.)
? It's my understanding, incidentally, that bovine calves give pretty excellent blowjobs, to the delight of many an experimentally-inclined pubescent farmhand. But you didn't hear / read it from me. Interestingly, most men are quicker to score themselves a wide-screen telly sooner than a calf. Maybe it's because the upkeep is cheaper.
Cultural influence can't be overlooked in discussing people's sexuality. 
