Simple reduction to essential/intrinsic characteristics is not idealism as it is generally understood. The use of the term "Ideal" obviously pushes us towards consideration of things which are to be preferred, specifically things which are perfect.
yes, this is a common thought: ("nature is not an ideal, but all that is") a thought which is based on bad idealism or ignorance of idealism (as i have defined it). basically an autistic lack of insight into one's own nature and into one's struggle with one's nature, and/or the failure to assume that other natural entities also have both own nature and a struggle with it. it's often those who are in denial about inner conflicts, who are unable to form true idealistic judgments. suddenly "everything is okay just as it is", because it's to painfull to think otherwise.
good idealism knows right away, that intrinsic and essential aka "natural" characteristics are not identical with all semi-intrinsic or somehow inner characteristics, that are apparently coming out of the inside/nature but are not essential (or not archetypal
for example - for lack of a batter word and without implying that everything is pre-programmed in static types)
a simple example: psychological health (aka integration) is an ideal (of nature), samsara is reality.
non-idealism parties in samsara, satanism style, idealism tries to find the covered pure potential underneath it all, while separating it from the rest. non-idealism assumes that there is only meaningless struggle and chaois, idealism insists that struggle is the educating difference between ideal and reality.
therefore no person who has any amount of idealistic intelligence would formulate at any stage of his/her development, that "
all values are
only relative to a culture" (which we hear a lot from ... i dunno ... but i believe lazy introverted thinking with poor extroverted intuition, during a specific stage)
of course values are in part relative to culture and in a more significant part relative to essential characteristics (the nature/brain/etc) of a particular person at a particular moment in growth. (at least blame some of our values on DNA, if you are a materialist/reductionist)