Ahh...well my thought of Aikido is what separates Aikido from martial arts is its non destructive philosophy ...
When I am talking about "keeping aikidō 'pure' " I don't refer to a certain philosophy. But to a certain form of body work. (Which I think by now is rooted deeply in daoist forms of cultivating one's body ... but that's another story ...) This way of using one's body and mind can only be learned using certain methods. Which have to be kept "pure" for that reason.
aiki as a technical method can be found in other budō and - what's more interesting, I think - in Chinese internal arts. There are even budō that explicetly use the term aiki like the KSR.