I think it's because you aren't exactly well-versed in Realmslore that you find this idea crazy, but there are precedents that make it clear that Faerunians have very different views from us about pain and mortality.
There also are precedents that make it clear that death is something unpleasant and most people try hard to avoid it as long as possible.
Examples you can see in this game itself ...
Nettie tryes to kill you > you (and some of your companions) get rightfully pissed.
Arabella is killed by Kagha > her mother gets rightfully pissed.
Lae'zel offers to kill you > you refuse.
Minthara kills whole grove > Wyll gets rightfully pissed.
And bzillion others.

I mean if people would be so cool about death in Faerun as you try to tell me, they would be quite cool with the fact that someone died around there ... he IS in better place now ... and if he isnt, he deserved it ... so what?

But that is not the case, is it?

When Kelemvor ascended to godhood, he reformed the Fugue Plane and the City of the Dead to clearly reflect alignments and reward afterlife accordingly (which he soon discovered was a dumb idea). People, especially good-aligned, were throwing their lives away left and right, because they knew they were going to this awesome place filled with happiness and joy. Tormites willingly committed suicide during the battle in Tantras to fuel Torm's power. Ilmatari clerics regularly sacrificed themselves in various ways to aid the needy and the poor (and especially to protect people from Banites and on occasion, Loviatans).
This all seems like fanatics giving their lives for greater cause ...
Nothing special even in our world ... yet it certainly isnt regular way to look at life and death.
The martyred champions of Ilmater were those who sacrificed themselves and came back to life by various means, so it shouldn't be a novel concept for the party to know that resurrection and restoration are available as options.
Since our party have countless potential chances to find out that when they get killed and ressurected the tadpole is still there ...
I dare to say they on the contrary can easily figure out that this option is simply not valid.
