Obviously if you've written a buggy parser then all bets are off, just as all bets are off if you've written bugs into any other part of your program. But those

Obviously if you've written a buggy parser then all bets are off, just as all bets are off if you've written bugs into any other part of your program. But those bugs would probably still be there if you didn't explicitly parse the input - they'd just appear later on, mixed in with your business logic which is performing ad-hoc parses whenever it needs the data!