(This is a "draft" answer because with more thought I can probably improve it.)
As Cypher says, use of あっての here is the same as that in the common Japanese saying:
命あっての物種[だ。]｜While there's life, there's hope. / It's not worth risking my life for.
Unfortunately this expression itself is, if not idiomatic, not gramatically intuitive either. もんだね is not directly translated in my dictionary but if we apply the Japanese definition I used in my answer to your previous question:
N1あってのN2＝N1があるから N2が成立する
to
命あっての物種
We get:
Because we have life we exist ~>
~> Something that exists because we have life ~>
~> [in the case of 登山・mountain climbing]"We would not be able to climb mountains if we were not alive" ~>
~> "life is more important that climbing mountains"
Now, rather than agonising over this expression further, I would suggest we look at the rest of the sentence:
..なのにと...
sounds like the conjunction for a "fact => an unexpected result" followed by a "quotative と”: The "unexpected result" appears to have been omitted because it can be inferred from the context of the passage from which this sentence has been taken. Without knowing the rest of the passage (see note 3 below), I would guess this omission is something along the lines of "people still do it", "people still do it without the proper equipment" or even perhaps "I could not bear to give it up".
If we put this all together we get:
"Everytime I read about people getting killed in the mountains, I am sadly reminded that even though mountain climbing is not worth risking your life, [people still do it without the proper equipment]."
Notes:
The omission is in [square parentheses].
I have taken a little literary license to translate "悲しく思う” as "sadly reminded".
This sounds like a sentence from a JLPT N1 exercise, in which case, this might be a stand alone sentence rather than an extract from a passage because the examiner wants you to go through the same thought process I have just taken you through here. (And, by the way, this is a great question.)
