While I agree that most people shouldn't put more than two clowns in a tank under 200 gallons, and that those clowns should be the same species, there are other variables to consider.
I match up clowns for breeding. In that respect, I will often put a large number of clowns in the same tank - sometimes even a 29gl, let them sort things out, and remove the runts as they begin to get picked on. This typically will leave me with three or five clowns - two of which will become the mated pair. I'm not sure why it has to be an odd number, but for me it has just always worked that way.
Also, the clowns do not need to be from the same hatch, and if breeding is a concern they should NOT be from the same hatch. They should all be around the same relative size, though. Usually I'll get one larger and the rest around the same smaller size. This will speed up the process as there's no question as to who the dominant fish is.
If you know what you're doing then there shouldn't be a problem. Eventually you learn what the different behavior of the fish means. You learn when they are violently fighting and just sparring for dominance. I had a mocha grab the tail of a fancy ocelllaris and spin him around a couple of weeks ago and immediately removed the fancy. This wasn't dominant behavior - it was violent.