I know what you mean, and actually yeah, most of the Red Lanterns were originally just that. Mindless rage monsters. However, in the wiki and in the comics, they've recently been changed so that they can have actual rational and coherent thoughts and do other things aside from just roar and spew napalm blood and stuff...

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Over complicated explanation. In short, while the Red Lanterns are powered and consumed by rage they are still capable of rational thought. Rankorr, one of the newer Lanterns was even shown to try and talk his way out of a fight he wanted no part in.