Well, we don't know if Guantanamo is used by the recruiters or not, but we don't believe that if those detained at Guantanamo suddenly were granted freedom or transferred to prison or detention in other countries or perhaps in places in the United States, that the stream of terrorists would dry up or the attacks against America would stop. We doubt if the President believes it either.
Many attacks took place before there even was a detention center at Guantanamo, and many attacks have occurred against targets in Europe, Africa, the Mid-East or Australia - and none of those places have their own "Guantanamos."
The important point is that detainees are not "typical prisoners." Inmates normally are released when their sentences are up or when they have met terms and have been awarded some type of parole, and one expects a certain percentage of recidivism. But in the cases od the detainees, we can almost guarantee recidivism. The detainees are not being released for good behavior or because their time is up, but instead are released when America can find someone else to take them off our hands. They are dangerous, but are being released in spite of that, and being released to satisfy the President's pledge, not for the interests of justice.
Current law, signed by President Obama, prohibits the transfer of detainees to the United States. Sad to say, that prohibition in and of itself will not stop the President from transferring them anyway, but such transfers would be illegal, and in defiance of Congress.
To sum up: closing Guantanamo will not remove America from the list of terrorist targets; it will not prevent former detainees from returning to the battlefield; and it is counter to current US law: three good reasons to keep the detainees in custody and to keep the Guantanamo Bay center in operation.