They knew he would follow the Ring, and that the Ring could only be destroyed in Mt. Doom. He knew the way, and would be captured and possibly tortured like he was in Mordor, thus he would bring the Ring to Mordor possibly... No matter what happened, there were no reasons for him to stay in Mordor. Why would he stay? What danger could he cause by getting out? (Little did they know of that great danger - it seemed harmless at the time, I'm sure.)
__________________
...take counsel with thyself, and remember who and what thou art.
|