That's an intellectual, rational approach to sex. A guy could feel that way too if he thought about it. But there are very few girls out there who get physically turned on at the thought of having a baby. Wanting to have a kid falls more under the "choice" or things you have control of category, whereas most people have very little control over their sexual urges.
That's just not how it works. This perpetuates an incorrect idea that a gay man is somehow "part girl". Hormone levels between gay and straight men are no different, with many gay men having very testosterone high levels and some straight men having very low. Most stereotypes which are typically associate with "gay" typically focus around men acting more like women (or women like men), effeminate personalities, over-the-top tastes (or butch and a fan of softball, in the case of lesbians), but most of these attitudes only exist because of the unequal treatment of gays in most parts of the world, which cultivates this mindset.
The same was true with slavery, where enslaved individuals were seen as more submissive, less ambitious, and less intelligent. Slaveholders would use racially motivated arguments saying that these people were enslaved because they were submissive, less ambitious, and less intelligent, but it is clear today after slavery has been abolished in America that these people were less driven because they were slaves, not the other way around. Gay people do not somehow act like their opposite gender in society because they were born that way, it's because most societies project that image upon them, and that's often all we see reflected back.
The fact that you don't believe in lesbianism I think just reflects on either a lack of encounters with actual lesbians, or just springs from your perspective as a guy. But trust me, lesbians exist outside of the realm of pay-per-view websites.