Oh boy, here we go. You all better read this whole post; my fingers are getting tired.
I... ... I completely disagree. 100%.
It is perfectly fine to feel one way about someone, and then grow to feel a different way about them.
Heck - take the girl/guy "date" thing out of it, and it's still true. There were kids I hated in elementary school that I grew to be friends with. I had friends early in college that I can't freaking stand now.
People change. Thus, feelings can change.
Hell - look at the divorce rate.
Okay, friends that you start to like over a really long period of time - like a decade or two - are another can of worms entirely. I've made friend relaunches work, but boy it takes a lot of effort and that's even without sex.
But these other traits that people change quicker than that: I'm not sure. I guess I don't trust people can change that quickly for the core elements of someone, which is what I assess when I'm looking at relationship material. It can happen, sure, but it's complicated and there's other people out there.
Clearly hardcastlemccormick is Martian. That explains how he would know everything about any female he wound up in a friendly relationship with to the point of knowing that they would make for excellent romantic partners before word one and how he would not understand feelings developing as you come to know more about a person. As we all know Martians are telepaths who walk around with their minds open to other Martians at all times.
Seriously though "Changing your mind is not natural" is the most ridiculous of statements. I get what you were shooting for, I don't disagree entirely, but you missed the mark by about 2 country miles.
Of course you're not sure if they're going to make good romantic partners. That's what dating is for.
You find out. You have to be open and looking. And of course you have a window in between meeting someone and asking them out (I hate cold asking out, personally), like a few weeks or so, which should be enough to get a taste.
Here's how I do it: Meet a girl. I come to the conclusion, after a few hours/days/weeks, that I like her. Flirt. She flirts back. I ask her out on a date. She accepts. We get to know each other better. Things go well. [Insert x amounts of dates until I have a good picture] I ask her on a more serious date involving my place. Heavier physical contact. Kiss. Making out. [insert x amount of dates that may be zero] Sex. More dates, more sex, relationship.
At any point I can bail out of the above steps. Then again, I'm not looking for someone that has to sync up with me perfectly. A don't need another Martian; maybe a Venusian or someone from the asteroid belt, I'm not picky.
That's exactly how people get into relationships with the same type of bad people. They set themselves on the same type of person because "that's what they like," and without experience there, how would they honestly know? Especially since no one's psychic - you don't know exactly what sort of person they are the moment you meet them. And what do you really have to go on? Don't judge a book by its cover applies. Feelings change all the time. Especially in a situation where you're hanging out with someone for a prolonged period of time.
EDIT: Pre-empted twice.
Metaphor time! Meeting a girl is like watching a teaser trailer for a movie. You've got a name and a synopsis, with a nice little "ooh that's nifty" feeling on top. This should be enough to at least allow you to decide if you'll watch the trailer, which is like a date. A longer look at someone. A good idea of what to expect. A relationship is going to see the actual movie.
Yes, you have to make judgments. Yes, you can be wrong; the trailer could be way better than the film. This is why you do all of this early and bail out if it turns out to read her wrong. You also give pretty much everybody the benefit of the doubt, because naturally some people are bad at communicating, but honestly I very much value open and decent communication in a relationship anyway. So.
Yeah, it takes a lot of damn work to find somebody, and it's hard work. But it does pay off.