"If The Collector cannot be trusted..." Those words disturbed Thor profoundly, The Collector was well known for saving rare creatures and antiquities from their destruction. "...then it is our duty to find somewhere to burry it. The gem wants to be used. It will be relentless in it's temptation."
Holding the gem around Thor was strange. He was old, as old or perhaps older than the Doctor, but there was a strange constant to his timeline. Thor had not grown or changed much, if at all, even with his newfound place on Earth.
"No mortal should have that burden," Thor said quietly. "Let me help you."