I'd have to disagree with that.
Plenty of people mix them, tank-raised fish generally tolerate a wider range of pH. People seem to have a thing about mixing cichlids from different continents, but will happily chuck a south american or asian bottom feeder in with their african cichlids.
I've never seen an african cichlid trying to attack anything through the glass like a large guapote will. Most large central american cichlids (jags, convicts, jack dempseys, texas, midas/rd etc) will defend a territory once mature, even when not breeding.
Dantezgirl, its well worth it to learn the proper/scientific names for fish, its not that hard and the more you do it the easier it gets. The fish you have listed come from pretty varied habitats, and it woudn't be a good idea to mix all of them. Have a think about the kind of tank you want to set up, ie planted community, rift lake biotope, mixed cichlid community etc.
Also, "americans" and "africans" are stupid terms to use. There are plenty of african cichlids that come from habitats outside of the rift lakes, and they vary considerably. "American" cichlids vary from tiny dwarf species that like soft acidic water to the largest cichlids on the planet that come from harder alkaline waters.