"Because they say so" and famous misattributed quotes.

One of the most annoying and lazy habits of some writers is to refer to the nebulous entity, “they”. “They say travel broadens the mind, ...” [1] "Don't listen to what they say ..." Nice sentiments, but who are 'they'? “They” are not a trusted source or reliable reference for any fact or assertion. Using “they” to reaffirm an opinion not only insults your readers by expecting them to just consume whatever you write (because you are such an authority), it is also puts on show your inability or unwillingness to actually research something properly. Okay, while it may be safely assumed that more than half your readers will just take your word for it, there is also a percentage who will ask, “says who?”. Thereafter, none of your writing carries any weight at all. Simply substituting ‘scientists’ or ‘critics’ doesn’t work either unless you can point to exactly who these learned individuals are. If quoting ‘studies’, then what studies performed by whom