Ok,
All fish are different, just as all people are different. Male and Female betta's are NOT killing machines. They go very nicely in community tanks due to the passive nature. All that is required to keep Betta's ina tank with other fish is a little ******* common sense. Agressive fish fight with agressive fish. Put a betta in with tiger barbs and you'll likely see some fighting. Put a betta in with another male betta, again you'll likely see some fighting. Put a betta in with a Jewel Cichlid, and you won't have a betta. However, bettas are passive when combined with other passive natured fish. For instance, I would recommend a betta ina community tank with tetras, such as glowlights or neons, or bleeding hearts and such.
The bottom line of Betta's being agressive is to do a little research and find out if you will be putting them in with other agressive fish. If their tankmates are normally peaceful, then you're probly ok. But as I stated at the beginning of this post, everyone is different. Maybe you will get a mean betta that will kill your friendly neons. Maybe you'll get a nice betta that won't fight with tiger barbs. Who knows. Its up to chance, however, agressive + agressive = fighting. Community + Community = Symbiance.
As for cups being cruel...
Yes, it isn't nice to put them in cups. But yesterday at Petcetera I received a shippment of 150 bettas. Now what would YOU do with 150 bettas? They have to be separated, and I only have one tank for bettas and that is for the females. So what do I have to do? Pull out the cups.
For your information, Siamese Fighting Fish (Bettas) have an organ in their head, called the labrynth organ, that allows them to proccess air. This means that bettas can absorb much more dissolved oxygen from water than other fish, and can even survive out of water for a few minutes without any harm. For this reason it is possible to put a betta in a cup of water, because he does not need a great ammount of water to provide the neccesary dissolved oxygen content for him to breathe. So long as the water in the cup is changed frequently, as in everyday, then waste buildup is negligable and the fish are just fine.
Ya, its cramped, but the rule of thumb for keeping fish is 1 inch of fish per gallon of water. That is for NORMAL fish, WITHOUT the labrynth organ! So if you were going to keep a neon tetra on its own, you'd be good to put it in a 1 gallon tank. A betta on the other hand would be happy in a betta hex, and what are those? 1/2 gallon? Not very much anyways, but it doesn't hurt the fish.
I'm arguing this from a scientific standpoint, but people love their pets and It is normal for an owner to want a nice habitat for their fish. But this argument about cups being mean and cruel, and a health hazard for other fish, thats a load of ****.
HooDude,
-The Petcetera Guy