Player feels he's being treated unfairly

[Emmerask]

A better question would be why the heck Kord should care about if a small spot on his Infinite plane should get unhallowed for a short while.

Personaly i think its bad gm'ing on the line of "rock falls, everybody dies"

Actions have consequences, establishing this is the mark of a good dm not a bad one.
And the rock falls everyone dies is not a good analogy because that is a completely random act while what happened is a consequence of an action.

Also if I remember correctly these infinite planes are also the home of infinite solars so spotting the culprit is not that far fetched, then Kord would send something that is certain to punish the wrongdoer, it really doesn´t matter what creature is send because it would be likely to deal with him swiftly anyway.

A good analogy would have been
DM: you are in a large cavern deep underground that seems to be supported by only one pillar in the middle...
Player: ...I DISINTEGRATE THE PILLAR!!!
DM: ...Rocks fall everyone dies...

If players do monumental stupid things then monumental stupid things happen to them, any dm who lets such things slip... well I would not play one second under them tbh because a game where actions can´t have negative consequences is pretty boring.

The only thing I can see which could have been handled a bit better is too actually ask the player if he REALLY wants to do that, especially if its a new player but that is all the reaction was okay because in the end it matters very little if a solar or other similarly powerful creature would have mopped the floor with the offender or an avatar of a deity.