Great discussion, mostly because this hits on one of my biggest qualms about the hobby. There are so many guidelines about keeping fish that people tend to take as absolutes. IMO, there are no absolutes in this hobby and there are plenty of exceptions to the rule. Well, within reason (e.g. fish need water to live is pretty absolute... i guess
).
Goldfish may prefer slightly cooler temps and tropical fish may prefer slightly warmer temps, but they can both tolerate a certain range of temps that both can inhabit. How is this any different than housing fish that prefer different ph ranges, hardness/softness, and other needs? Most of us don't bat an eye when we hear about people keeping neon tetras with mollies.
I understand that we're just looking out for the welfare of the fish and are just trying educate others on what we perceive to be the correct way of doing things. However, I think the hobby could benefit from being a little bit more flexible and open-minded to different possibilities with regard to keeping fish.
Having said that, I'd love to one day take a pair of sibling male bettas raised together since birth, transfer them into a heavily planted 75g. tank for the remainder of their lives, and document it if successful.

Goldfish may prefer slightly cooler temps and tropical fish may prefer slightly warmer temps, but they can both tolerate a certain range of temps that both can inhabit. How is this any different than housing fish that prefer different ph ranges, hardness/softness, and other needs? Most of us don't bat an eye when we hear about people keeping neon tetras with mollies.
I understand that we're just looking out for the welfare of the fish and are just trying educate others on what we perceive to be the correct way of doing things. However, I think the hobby could benefit from being a little bit more flexible and open-minded to different possibilities with regard to keeping fish.
Having said that, I'd love to one day take a pair of sibling male bettas raised together since birth, transfer them into a heavily planted 75g. tank for the remainder of their lives, and document it if successful.