Niseno-Kami

In 2D it's thigh highs, which translates to yoga pants in 3D.

Are they? Weird. I'm pretty sure I usually suck at arguing. People do seem to generally agree with me even when I suck, though. I don't get it  
My point is mostly related to how much of that process is actually considering their ideas.
There's a very big difference in my mindset if I decide to learn some math, read philosophy on something I don't know about or talk to a holocaust denier, for example. 
In the first case (learning math), I'm not going to question anything I'm learning. Because math is math, and I'd be dealing with a set of rules. I won't question any formulas. They're there and they're right and that's it- the thought to disagree with that doesn't even cross my mind.
In the second case (reading philosophy), I'm considering completely new ideas (to me) that I don't have any knowledge or opinion on before reading. I might end up agreeing or disagreeing with them in the end, but I'll seriously think about everything I'm reading with an open mind.
The third case, however (talking to a holocaust denier) is very, very different than the first two. Because I already think everything that person will say is bs before we start talking. I'll probably also think they're scum or just plain crazy. Therefore, I find it impossible in me to consider their ideas seriously.
You mentioned that being open minded is related to "thinking about something carefully before making a choice" - In both the first and third case, I wouldn't do that at all. To me, the first is true before I know anything about it, and the third is wrong before I know anything about it too. 
You also mentioned that I have knowledge on why people thought races are different (and presumably on the other subjects I said I wouldn't consider, too) - But really, do I?
I, for example, never heard the evidence of the holocaust. I know it happened and people say everything was extensively documented, but I never checked that out. I just said "mkay, that's it, then". I don't even know the exact timespan of the holocaust, but considering it began in 1933 and lasted till 1945, that's 4380 days of nazis killing jews... Which is about 1400 jews killed daily for 12 years straight. An absolutely astounding number, that just goes to show how messed up the nazi regime was.
I have absolutely no doubt the holocaust happened, and that 6 million jews were killed during it. But it's not like I have a lot to back that up, because I never studied the holocaust. I've been told everything was extensively documented and that's good enough for me. It's not like I have seen the evidence for it, because I just didn't bother enough. And yet, without seeing any evidence of it at all,  I am completely closed to the idea that the holocaust might not have happened. Because that's just ridiculous, right?
Same for white supremacy or ISIS. I never looked into why white supremacists think what they do. It just sounds ridiculous to me from the very start- therefore, I don't give any thought to that. And ISIS. Who knows, if I read the Quran and talked to whatever their equivalent of a priest is I'd agree with them. All the media I see on them is heavily biased against them, and it's not like I ever looked at things from their point of view. 
I reject all sorts of ideas that I don't really know anything about daily. And in the cases where I don't flat out reject them, I learn about them while being biased towards one side, heavily or not. I am much more likely to accept ideas that stick well with my lifestyl, community e and social circles than I am to consider ideas that don't. I am much more open to politicians who're in the same side of the spectrum as me than I am of the opposition. Even when they have perfectly valid arguments, I probably am very likely to disagree first and then find excuses for rejecting that idea later, while ignoring possible evidence that would back up the idea or plan of politician X. 
Therefore, I find myself much more open for certain ideas than others, and not based on knowledge or argumentation, but rather bias and convenience... And most of the time, I don't even realize it, as I think most people don't when it happens to them. 

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If you'll let me keep my little rambling on for some more time, how about I try saying even that's a bit too vague to be meaningful? 
Are there people who'd be open-minded to ->any<- political, social or spiritual idea? Were I to tell these open-minded people that Hitler was the greatest person alive, or that all africans are no more than cattle, or that the voices in my head tell me I should kill all non-believers any serious thought?
If someone approached me with any of those ideas, I wouldn't even think about it, even if I pretended I did. After all, it's ridiculous, right? Clearly so. We all could come up with 1000000 reasons to say it's ridiculous, but even before giving them any thought, just listening to the idea loops me to the conclusion that "that's ridiculous". And so, while thinking about it, I'm not giving the ideas any chance of being valid, or seriously considering them- I'm just looking for reasons to explain why they're ridiculous, an idea that had been on my mind from the very start, before I even had any arguments to defend it. 
Those are all very extreme examples, but I'm certainly biased against a great many other things which will make it impossible for me to give them any serious thought. For example, whille I see democracy as a failing system, I'm unwilling to seriously consider any other governments. I can only think about it for a few minutes before coming to the conclusion that "that's ridiculous"- and I'm sure supporters of a monarchy or any other system would be able to refute my half-assed reasons that were born out of very short thinking pretty well.
I'm also unwilling to consider the thought that races are inherently different. All human beings are equal, right? Thus, if you were to tell me that africans are inferior, I wouldn't buy it. From the very start, I would think all sorts of things about you. You could try giving me studies or literature to argue for your point, but I wouldn't read any of that. I'd just call you racist, and be done with thinking about the idea. 
Same with what's happening to ISIS. I've never heard their viewpoint.. I've never read their holy texts. I've never talked to any muslim, much less extreme ones. But if someone told me that I should consider they may be right, I'd just think that person is crazy.
 
I'm unable to consider the vast majority of things that go against my pre-conceived notions of equality, morals, philosophy and whatnot. And I recon I don't even know most of the things I'm biased against. It just happens subconsciously. And that bias may be a good thing. No one should give thought to religious extremists or racists or plain crazy people, right?  Is it bad that I don't?
 
Again, feel free to ignore my rambling. Maybe I'm just crazy, or drawing bad parallels or something. I dunno. 

Hopeless senpai is so hopeless 

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Hah! Well said. You are fitting in here just nicely
 
Thank you Tay, we all love you.