Generally, when people say "Betta", they refer to splendens.
When it comes to fighting, I think we have the same problem as we have with pit bulls, on a less complex level. The dogs were bred to fight, and fighting is still an underground thing in some places, and less so in others. Some pitties are aggressive. I walk my old dog in the woods, and every single dog on dog attack I have seen there involved a pit bull as the attacker, and as the dog drawing blood. People will tell me what I've seen isn't real, that's it's not true and it's nature and nurture, but I suspect in those cases both nurture and nature were issues.
Completely agree here. I made a real essay reply all about pitbulls and the nature/nurture debate, since it gets heated with neither side willing to face reality and understand each other. And as with most nature or nurture debates, it's almost always a mixture of both.
We've selectively bred dogs for centuries to do certain tasks for us. No one is surprised when a greyhound loves to run and chase small fluffies, or a Border Collie has a natural tendency to herd, which is then built on and improved by the shepherds training. Pointers naturally go into a point when they spot a bird, retrievers usually retrieve well and love water, etc etc! The list goes on and on.
While of course each dog is an individual, and not all are cut out for the work they were bred for, or have come from pet only lines and changed the breed somewhat, there's no heated debate about how other breeds have breed tendencies as a result of their genetics. That potential owners need to be aware of and decide whether it's the breed for them, and if they can handle a dog like that. A little old granny living in a flat doesn't need to be getting a livestock guardian dog, you know? Pitbulls are not some special exception where they're a blank slate, shaped only by environment. There is so clearly a difference between a pitty and a Goldie in their basic nature, and denying it seems like flat earth believing, frankly. Wanting to believe against all evidence and reason.
I'm sure that with careful breeding by passionate breeders who wanted to save the breed, that the aggressive tendencies could be reduced by a great deal. The pitties strength, determination, high prey drive (gameness, in dog fighting terms) makes them a very high risk to other dogs, and sadly, too often to people as well. But most pitties in shelters come from backyard breeders. Idiots breeding for size/colour/profitability, not temperament. While the dog fighters continue to breed their most aggressive and game dogs, with their stock often going into shelters and then pet homes when the ring is raided and the dogs rescued.
The question would be who will change the breeding plan for these dogs, and breeding out all of those breed tendencies would also change the shape and nature of the breed entirely. It would no longer really be a pit bull. I don't see the pit bull advocates going for that. So I'll keep steering clear of them when I'm out with my own dogs, since one of mine was almost killed by a staffy. I never want to go through that again.