"Please give us a simple answer, so that we don't have to think, because if we think, we might find answers that don't fit the way we want the world to be."
~ Terry Pratchett in Nation
The echo is not inserting the slash. The slash is (most likely) due to the data being output coming from a form input, and your installation of PHP (correctly) having "magic quotes" enabled. In any case, the stripslashes function will remove those slashes. To make the code portable (in case it's ever on a server where "magic quotes" are not enabled), you can do something like:
"Please give us a simple answer, so that we don't have to think, because if we think, we might find answers that don't fit the way we want the world to be."
~ Terry Pratchett in Nation
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