We now know there is an angel powering the blade, which knows what it is doing, this why some Knights serve foe decades and some for days and how the faithsabre can cut an anvil, or a monster but not Sanya.
It would permit Thomas to touch the sword, but would have been inactive, it detects the intention of the wielder and of any person or monster against whom it is wielded.
Things like wedding rings are purely passive, they hurt Whamps nothing to be done and mortals can’t control the True Love effect on a Whamp, only withdraw their touch but an angel can, the sword is not a passive wedding ring, nor a control less mortal.