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Can anyone (perhaps an SJW or liberal who is expert in such things) explain to me the difference between "bisɛҳuąƖ" and "pansɛҳuąƖ"? There are only 2 genders, therefore only 2 possible scenarios when it comes to copulation or anything else.  Therefore "bi" and "pan" are the same thing.
In a similar vein, please describe what the "3rd gender" is. Everything is explained in terms of male and female, because those are the only concepts of gender that exist in nature.

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The difference is based in the thing called "binary sɛҳuąƖity." When you say, "There are only 2 [sexes], therefore only 2 possible scenarios..." you are practicing binary sɛҳuąƖity thinking (which is not wrong or problematic, just what it is). 
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People who say they are "pansɛҳuąƖ" or those who sympathize with them, have decided that they deny the reality of the two sexes, such that they deny the "two-ness" of sɛҳuąƖity, believing instead that there are "more than two," and they have made that denial the basis of their grasp on reality. It is an offshoot of Modernism, which has as its fundamental principle that "reality is in the mind." 
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In their reality, which they believe is in their mind, they have chosen to say, "there are not merely two sexes, but rather there is no limit on the number of sexes that are possible." BTW when they speak about these things they replace sex with gender, which you have done as well, in your post here. Perhaps without knowing it, you are conforming to their agenda by using their terms. To overcome this defective thinking you have to replace the word "gender" in what you read or hear with the word "sex," which is what they're really trying to say but think they know better, because to them they have redefined sɛҳuąƖ intercourse to mean sex, so as to accommodate all their sɛҳuąƖ perversions which might not have anything to do with sɛҳuąƖ intercourse, but rather includes whatever activity or process they choose to mean sɛҳuąƖ activity because limiting that is a further kind of narrow-mindedness like binary sɛҳuąƖity thinking is. Consequently "the 3rd gender" (they mean the 3rd sex) means whatever they want it to mean, because to them there are not merely 3, but rather the number has no limit. There could be 7 sexes or 27 sexes or 1,093,271 sexes. Who cares? 
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So it's not limited to 3 instead of 2, for they want to say how many sexes there are cannot be given a number, because to number it is to limit it.
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To think that it is possible to quantify the number of sexes necessarily limits your thinking, and they don't want to have any limits.
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To these Modernists, rebellion against everything and anything is a wide open possibility, for they believe that anything traditional is wrong by the fact that it's traditional. They are all about re-making the world in their own image as they please, just to be rebellious. Whether they realize it or not, they are acting as tools of the devil, who is all about inverting the truth, and reversing everything, turning reality on its head.

The problem is, the very SECOND LETTER of "LGBTQIA+++++OU812" stands for "bisɛҳuąƖ".

BisɛҳuąƖ is very much still a thing. In the huge charts of the various "orientations", bisɛҳuąƖ and pansɛҳuąƖ both appear. What's the difference?

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The difference is, bisɛҳuąƖ is passe, outdated, limited, old hat. It's not liberal enough. To replace it is pansɛҳuąƖ, which is without limits.

The term pansɛҳuąƖ was originally used by sigmund Freud to define sɛҳuąƖity as the basic drive for all human interaction.

Please don't quote that perverted hymie on this forum.

The term "pansɛҳuąƖ" has been getting a lot of attention lately, thanks to celebrities like Janelle Monae and Miley Cyrus, who have opened up about being pansɛҳuąƖ.

There is a great element of unbridled attention - seeking behavior behind all this.

Often times, it is all there is. 

I notice people (especially, women) nowadays would do or say anything, just to get attention. Even negative attention. Anything is better than being ignored. This is also evident in the deranged behaviors of the political Left. When they find it impossible to get positive attention or become aware of losing power and becoming invisible, these people usually go to great extents just to be noticed, even in a negative or repulsive way.     

Anything of a sɛҳuąƖ nature easily accomplishes this effect because most humans are easily drawn and manipulated through sex - men and women for different reasons. (See Dr. Michael E. Jones talks on this topic, about the clever use of pornography to utterly demoralize and control an entire nation).

You have to move.  It is the only way to get rid of memories and bad influences from peers.  MOVE. 

So if I understand this correctly, "pansɛҳuąƖism" is just the politically correct version of "bisɛҳuąƖism."  Like how "transgender" is the politically correct term for "mentally ill degeneracy"?