There is no golden rule of how many fish you can keep in a tank. People read these rules and preach them having never seen any of the aquascaping, distinct personalities of a specific fish and overall size of the specimen at the time.
These rules are rough estimates and aren't always accurate. They are based on general teritorial concerns and your systems ability to filter the wastes the animals produce. You need to observe the fish that you have in the aquarium, if they are showing sign of aggression and being teritorial, then there is a good chance the new fish recently added is causing some serious stress and things need to re-evaluated. Without fully knowing what a persons setup is (ie lbs of live rock, quality of skimmer, husbandry practices etc..), it is hard to tell someone that it is unethical and impossible to keep that many fish in a system. Is it recommended? maybe not, is it possible, without some form of stress and overall health detriments to the fish? certainly.
Keep in mind, that when your fish get bigger, you also gotta start re-evaluating your livestock and their requirements. If you have juvenile tangs, you'll be able to get away with it more until they grow bigger and need more room.
Just because you have a 50 gallon tank doesn't mean you get to have 10" of fish EXACTLY! You may get some very "nice" specimens that aren't territorial and be able to get much more with proper husbandry techniques and equipment. On the other hand, depending on the fish you get, you may get less than you hoped for, even when others tought your list was a light to medium load.
I agree that you have too many fish AT ONCE.....way too many, but people gotta stop preaching these rules of thumb like its the end all, be all to responsible fish keeping.
sorry for the rant, I maybe in a little bit of a foul mood