Indeed, bisexuality and pansexuality can mean the same, but do not always mean the same. They are rather alike and I believe majority of bisexuals also discard the gender binary in regards to sexual attraction.
Bisexuality is a sexual orientation where one is attracted to the same gender and other gender(s). Which means it can be two gender, it can be three genders or it can be all genders.
Pansexuality, or omnisexuality, is sexual attraction, sexual desire, romantic love, or emotional attraction toward people of all gender identities and biological sexes.
I don’t have anything against bisexuality at all, I do notice that a lot of genderism occurs when explaining sexualities which include attraction to more than one gender, especially bisexuality due to the bi prefix. I try to correct this to others whenever I can, but there are a large variety of ways the world defines bisexuality.
Like the figure above shows, it overlaps. In my own story, I just felt immediately drawn to pansexuality myself because I wanted to completely remove physical gender from the equation all together.
There are more similarities than differences between bisexuality and pansexuality. I don’t really see it as a mess as I definitely support anyone with whatever sexuality or sexual preference, I merely want to educate people of the sexualities commonly used nowadays.
I think many people do try and define bisexuality in a binary method in order to establish the difference between the two when explaining pansexuality, but they are more like fraternal twins; incredibly similar with (sometimes) slight differences - also depending on how you see both. In my case, I was feeling the pansexuality one more than the other.
I hope that explains it to you from my view point. In regards to the fact that there are labels, a lot of people who do not feel within the society’s norm will choose a label they connect the most to which allows them to find a like minded community of peers. It is a primal programmed activity of our minds in order to protect ourselves ~ like safety in numbers.
If you have any more questions, do not hesitate to ask.