I'm about to drop some heavy science on you guys. And it's in regards to a topic some of you may be made uncomfortable by. Others my be offended by the facts I present. Don't get defensive. This is just how things are in the real world.
DISCLAIMER: The subject matter isn't really for minors.
The term is "dudes with boobs" not "chicks with dicks". That only happens in the event of a gynandromorph. These only occur in some species of arthropods (especially lobsters and Lepidoptera) as well as a FEW species of bird and lizards. the closest thing to a female having a penis in Mammalia occurs in hyenas. And (for obvious reasons) makes birthing rather difficult. So the trait ends up being in similar circumstances to a buck's antler size; while being selected for sexually, it's selected against logistically.
For those of you who will undoubtedly bring up all of the pictures you've seen of real "women" with penises, that's called Klinefelter syndrome. Males born with an extra X chromosome will frequently have hormonal imbalance issues, which can lead to the guy developing breasts. For those of you who've never taken a genetics class, in mammals (ALL MAMMALS) the sex of an individual is determined by a portion of the y chromosome known as the zinc finger on the y (or ZFY). If that's present, the individual is male as it prevents Müllerian development (formation of uterus, cervix, and vagina). Before anyone asks; "yes" if the ZFY fragment is attached to an X chromosome and the genotype is XX, the individual is a male, and "no" they WILL NOT have a penis (a different part of the y chromosome codes for that). Neither will they have a true vagina, cervix, or uterus thanks to the anti-Müllerian hormone signaled for production by the ZFY. There is a similar (but not the same) situation with a histological disorder known as Androgen insensitivity syndrome. Men with AIS (yes, they are all still men because they still have the ZFY) lack receptors to one or more androgenic hormones (male hormones) and thus will have a variety of developmental complications the degree to which depends on the number of receptors they lack. Some men with AIS develop bodies that externally look female due to lacking several androgenic hormones receptors. This doesn't happen with all men who have AIS (read the article).
So, if you want to make futa, you'd better be slapping breasts on male characters, not dongs on female characters. Or be into asymmetrical furries.
BTW: if you're into futa and really want to hate me, read up on the psychological implications of it.