There are some disturbing trends being advocated in this thread, and I will comment on those if I may be permitted.
Betta are not community fish. That doesn't mean a Betta may not work in this or that aquarium with other fish. It simply means than by their inherent nature, they are not suitable in community aquaria. And there are two reasons.
One is the personality of the Betta. It has been selectively bred over generations to be nasty. Why some Betta seem to tolerate certain other fish is not something we know the answer to. We do know that certain tankmates will enrage any Betta.
The reverse is also problematic. The Betta is often the target of other fish.
And in both of the above, we must remember than observable physical interaction is not the only thing to watch out for; the fish are sending out chemical signals, pheromones to their own species and allomones to others, and other fish read these. Significant stress is caused just by these, and we cannot see them or measure for them. But they are there, affecting the fish.
Experience doesn't always teach us correctly either. We are wiser to assume the norm rather than the exception. We learn more, and better, from the wisdom of those who know the subject. I don't need to drive my car off a cliff to find out what is going to happen. Nor am I going to start smoking to see if I will be "lucky" and be among the minority that will not contract cancer. And similarly I do not advocate taking risks with fish, which are living creatures and deserve the best we can provide. Read the blue paragraph in my signature.