Many people of the were interested in the theory of Eugenics.  It was an early science based on genetics  on the verge of the age of science.  It was of course bastardized by what was the last stages of the era of Nationalism.  Nationalism started out as simple pride of one's country and the efforts for it to be better.  Blue Danube, Grieg, Remington, Ford.  Roosevelt was entirely interested in Science and was a blatant conservationist.  He was great friends with a Black cavalry officer who was in charge of protecting Yosemite.

The letter you linked to is his interest in Eugenics as a science, not as a display of "blatant racism" as you so incorrectly assert.  I get that a lot of low level thinkers will argue that because he discusses the cultural differences amongst the human race is somehow racist, but here is the hate speech that defines racism?  

Note that Hitler completely misappropriated what was then a old concept of National spirit into what would be called Nationalist exclusion - i.e. racism.  But to call Teddy, or anyone else from that era a racist, is simply wrong.  

Its a bad thing to reach a conclusion and then try and argue in support of it.  That is not science or logical.