Totoally rubbish because employers do not take into account travel or housing expenses when deciding wages, only the employee does that which is known as 'wage negotiations'. the fact you brought it up will prove that employers will use it as an excuse to drive down wages.
Consider a place like Silicon Valley, where the influx of software engineers has pushed the prices of housing sky high. So even though tech companies located there pay their employees very handsomely, it’s a necessity because a lot of that money ends up going towards rent. So their spending power is not as strong as their salary would otherwise indicate.
If you are going to work remotely and don’t have to contend with the higher costs of living in a place like Silicon Valley, why then should said company pay them as much? They could cut salary by as much as say, 30-40%, which would still translate into a comfortable standard of living in a less costly state (I admit I am not familiar enough with US states to cite an example, but you get my point).
The alternative is that there would be someone else willing to do the same job for less money (and they would also be willing to accept less pay because they don’t have to move and uproot themselves).
Likewise, if geography doesn’t matter, and assuming everyone can do as good a job, what’s stopping facebook or google from hiring cheaper labour from another country?
The people clamouring for 100% WFH arrangement can’t see the forest for the trees.