Central to the dispute is that there are at least two different motivations for using "pansexual". The first motivation is a political one: "pansexual" is thought to be better or more inclusive than "bisexual". The second motivation is to actually make a distinction between bisexual and pansexual patterns of attraction.
These two motivations are in conflict. On the one hand, you have people who use bisexual and pansexual to refer to different patterns of attraction. On the other hand, you have people (not necessarily the same people) who say that "bisexual" is problematic. If we take both ideas seriously, the takeaway message is that some people are naturally bisexual, and their very existence is problematic. That's not what anybody is trying to say, but we managed to say it anyway with the power of teamwork.
To determine the best resolution, we need to take a deeper look into the two meanings of pansexual.
The political problem with "bisexual" is that "bi" suggests two. Two what? Genders? The trouble is that there are lots of people (henceforth "non-binary people") who do not fall into the boxes of "men" and "women". People can be between men and women, or be both, or neither. "Bisexual" was obviously created in a time when people just didn't think about that stuff. "Pansexual" is a better word because it doesn't have the assumption of two genders.
But there are counterarguments. One is that "bi" can refer to "same gender" and "different genders" rather than "men" and "women". This removes the assumption of two genders, even if it was there earlier in the word's history. People have also argued that there is a major cost to insisting that a group, whose major obstacle is invisibility, relinquish their most visible word (eg see Julia Serano, and also I've made some general arguments about the costs of language reform).
Some people have taken "pansexual" in a different direction, saying that it describes different patterns of attraction from "bisexual". For example, consider this illustrated definition:
That's something I made in 2013, although I'm not sure how much I stand by it. In general, when people make definitional distinctions between bisexual and pansexual, they pick and choose from the following ideas:
- Bisexual people are not attracted to non-binary genders
- Pansexual people are necessarily attracted to non-binary genders
- Pansexual people are attracted to all genders equally (ie to the same degree)
- Pansexual people are attracted to all genders in the same ways
- Pansexual people don't "see" gender in their attraction
- Pansexuality may be mutually exclusive with bisexuality, a subset, or an overlapping group
I also think that most people just don't know whether they're attracted to non-binary people, except by extrapolation. If I say I'm attracted to women, that might mean that out of every ten women, I find one of them attractive. So let's suppose that I'm very unusual: not only is my best friend non-binary, all five of my best friends are non-binary. And I'm not attracted to any of them. How can I know whether I'm attracted to non-binary people or not? (And it gets even messier when we realize that there are multiple non-binary genders.)
Therefore, I'm not sure how useful these definitional distinctions really are. What good does it do us to separate out people based on their attraction to non-binary people? I think in practice, most people don't really know, and are choosing their label based on politics. And what good does it do to have a separate label for people who are attracted to all genders equally? Are there any unique issues associated with this equal-attraction experience, as opposed to the general bisexual experience?
I have mixed feelings about pansexuality. I really hate to minimize the way that non-binary people are erased by our basic language, but I also hate the way that proponents of "pansexual" minimize the difficulties associated with getting rid of "bisexual". It's tempting to depoliticize the word and say that pansexual and bisexual simply refer to different groups. But I'm not sure there's much use in distinguishing between pansexual and bisexual patterns of attraction.
Note that "pansexual" is not alone in having two conflicting definitions. A much more infamous example is "queer". People use "queer" for the radical political connotations, but they also use it as a way of including a larger group without having to specify every letter in the alphabet soup. This is a cause of much conflict, although you'll notice that it hasn't stopped me from using "queer" on a regular basis.