Should beans be drained after cooking?
It depends what you want to do with the beans. 


If you cook dried beans in chilli stew, or similar dishes, you don't have cooking water, you have sauce, which is meant to be eaten. This applies to many other dishes, and of course soup. 
If you want to make bean burgers, you need to drain them fairly well or you end up with even more of a sticky mess when forming them. 
If you're making hummus, you should drain the chickpeas (garbanzo beans) and reserve some of the water to adjust the consistency.


If you're eating them fairly plain, it's up to you whether you want to eat something very wet or not, and that might depend on what else is on your plate. If having them wet alone, over rice or something like that, I'd try not to use too much water, and season it with garlic, herbs, chillies etc., or use stock in place of some of the water.