I agree with you on the point that Viagra isn't a necessity...
the same argument can be made with birth control and abortions...
Who gets to decide what is and isn't covered?
I'm sure there are some who would say gender transformation should not be covered.
I don't know if a lot rhyme or reason goes into the decision of what is and what isn't covered. I'm sure the cost of covering a particular ailment comes into play
and how prevalent it is.