Jikan wrote:"western" and "rational" isn't a problem in itself. It becomes problematic when it becomes reductive, as when one concludes that things one doesn't understand must not exist or must be false.
Yes, exactly! One can have his Buddhist sutras and his Stephen Hawking books, too! Lol
The Dalai Lama holds many traditional Buddhist viewpoints, yet he still delights in new scientific information.
Back to the original quote in the OP:
The author simply points out that deity yoga has some ordinary benefits which can be explained in terms of western psychology, but this doesn't disprove the fact that deity yoga can also have extraordinary benefits.
There are a variety of views one could have about deities being "part of oneself": some are beneficial; some are not.
1) One could have the view that the author of the original quote has (that a Buddhist deity is just a symbol of something positive in his mind). This view is slightly positive and might, therefore, be slightly beneficial, but this view doesn't give a person much power to transform his or her mind.
2) One could have the view that one's ordinary personality and body is really a Buddhist deity (like a schizophrenic person might believe). Such delusions will probably only have negative effects.
3) One could have the traditional Vajrayana viewpoint that a Buddhist deity represents one' inner Buddha-nature. This allows more positive transformation of the mind to occur, especially when seeing one's guru as a Buddhist deity.
4) One could take the more simple Buddhist viewpoint that the Buddhist deity exists outside oneself and that benefits can be obtained by meditating on the deity or from giving offerings to the deity. Whether the deity in question is "Real" or "not real," such practices are still beneficial.
So perhaps it's sometimes more useful to view things from a "harm vs. benefit" perspective, instead of a "real vs. unreal" perspective. And in regard to the OP, will "myth-busting the bodhisattvas" bring your mind closer to permanent happiness or bring it farther from it?