Its a valid question without doubt.
Before i got into MTB'ing. i walked into tredz and was astounded that people even contemplate spending thousands on a bike.
But then, i discovered Afan Valley, (literally 15min drive from my house and i had never heard of it) went up there on a £400 Gt Avalanche and loved it!!
Then you start reading about bikes, and start picking up on things, i.e. shimano groupsets, lx, slx, xt etc. Suspension, mmm, fox looks awesome. Ohh, full sus? carbonfibre?? I was like a kid in a sweet shop.
Suddenly i wanted a bike with full xt groupset. i wanted full sus, preferably fox front and rear, then i wanted carbon etc. I ended up buying a Zesty 514.
Is it justified in terms of matching my abilities? Definatley not! Is it justified in terms of, can i afford it, does it have everything i wanted, and would i have felt like i had 'settled' if id have gone for a lesser bike? Then absolutley.
So to me, its justified. To the average man in the street who doesnt know what it is, its just stupid money.
End of the day, more you know, the more you want. the more you want, the more your willing to stretch your budget.
At least, thats all true for me anyway.