Actually rooting is not the same as carrier unlocking either (which can commonly be done without root). And one of the things blacklists are for is dealing with people who break contracts (if they don't work properly in your country that's the failure of your operators). In many countries IMEI modification is illegal by the way (which is fail enough, since I struggle to think of a legitimate reason for that. Oh, and that's also different from rooting). I've rooted in the past in order to have better backup capabilities, better firewalling, make changes to the ROM or kernel to optimise the phone for my uses, and to make it possible to update devices after the manufacturer stops supporting them or to install a lighter operating system without the manufacturer's bloat. There are many legitimate reasons for rooting.