I have to agree with Dan, and I don't think it's any different for African cichlids (Malawi, in my case). Yes, they are agressive, but no further than the next male competitor that is too close to their territory. Especially with Malawi Mbuna it's really easy: if the competitor is not able to move away far enough from the dominant male, he will usually die - either swiftly or slowly.
Some agression can probably not be avoided in any tank with more than one cichlid, but continious or extreme agression is usually due to a tank being too small for what you want with it (keeping species that need a large space for their territory), mistakes in the stocking of the tank (putting species together that shouldn't be in the same tank), or even a mistake in decorating the tank (two species and only one obvious place for a territory), or a combination of the above.
Overstocking a tank with African cichlids is common, and it does allow you to keep more fish than you would ideally be able to, as indeed the agression will spread over multiple fish. However, if behaviour is what you want to see, overstocking is not the right way to do it, as overstocking will (at least partially) surpress the natural behaviour. And behaviour was - at least for me - one of the reasons to keep cichlids instead of 'normal' tropical fishies (with all due respect)
When I am done re-organizing my tank, I will only have 3 or 4 species in a (approx.) 170 gallon tank, and none of these fish is larger than 7". I started with 6 or 7 species, and less is really more in my opinion.
If lots of species & lots of colour is what you want, overstock your Malawi tank. If you want to see their actual behaviour, keep your fish in a configuration like you could encounter in lake Malawi itself, and make sure they have enough room to show it! But I realize that this is probably a very 'European' view of keeping cichlids. I am not saying one way or the other is better or worse, but I do know what I like best myself