I think we need to clarify what we mean by dying "al-kiddush Hashem".
If the question is: when is one required to give up one's life for Hashem,
then there is a definite halachic answer to this.
However, if you are asking about the common practice of saying that people
have died "al-kiddush Hashem" then this is really a moot point. The term
means that the person's death was a "sanctification of God's name". If
a non-religious Jew died in the holocaust, or an Israeli soldier died in
an accident, is it any less of a sanctification of God's name? Does
it really make sense to start ranking people's deaths to see whose death
was more of a sanctification?
Besides, if any one person thinks that someone's death sanctifies the name,
then by definition, it did.
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