yes but that relies on the idea that the word gay is used only to describe someone of a homosexual nature. surely we should then also discourage the use of 'gay' to mean happy, for fear of the demograph being labelled as overly-joyous and irritatingly positive.  
my point is gay isn't just used to refer to a homosexual; just as it is/used to be used as a word for happy or joyous, it is also a term for something of a negative nature. while this is a result of homophobia in the past integrating the word into our vocabulary as strikingly negative, it's connortations today are not the same.  
the n-word was never introduced into english as anything other than a direct insult towards black people. the g-word has developed - albeit unfortunately - into a generic insult for all things. 
 
comparing someone saying "eww thats gay" and someone directing at a gay person "eww you're gay" is using two different meanings of the word. the former is simply expressing distaste in something, the latter is describing being gay with the word 'eww' 
 
and let's be honest, serious homphobes aren't quietly going "isn't it great how we can call things gay and get away with it!" - the bigots you talk of have a list of much more offensive homophobic words to use - and do use - rather than simply 'gay'

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