I don't get your point. open could cause havoc as well if you've botched up the second argument (or third if you use three arg open). Is that the fault of open? If you match a regex against a string you've botched up, you get the wrong result. Does that mean matching has an "ugly" side? If you pass in the wrong arguments, most functions will do the wrong thing - but that's not the fault of said function. It's the fault of the caller of said functions.
Let me quote an early computer pioneer:
On two occasions I have been asked, 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.