Arthur's Progenitor Authority was what let him maintain the entrance to the Veil, so he could not switch it off, but it was also what was screaming at him to touch the crystal.
'Just a little touch…just the tip of your finger…a tiny tap…just for a second.'
Arthur felt like he could hear voices in his head telling him these things and they were getting louder by the second.
Telling him to touch the crystal in front of him…the Titan god's Divine Spark.
'The best decision would be to switch it off, but that'd trap us in here.'
The veil they passed through to get to this body was meant to keep things inside, so it was stronger from the inside than from the outside.
Arthur doubted he'd be able to tear open an exit in the Veil if the one he created from the outside was to close.
This situation made Arthur heave an exasperated sigh.
"…dude? You good?"