Like most things "it depends"
Is some edm cheesy and rubbish, yes definitely. But then that's true of all genres.
My simple basic understanding is edm is pop music with a Base line. Pure Techno is just the Base line with everything else in between (or encompassing )
Do I think it's horrible? No I actually like a lot of the quality stuff, usually because it has good lyrics you can find meaning in and attach to with a beat (Calvin Harris - Under Control for example). And so do many others judging by what sells out and ticket prices.
Would I listen to it 100% of the time? No cause I get bored if something is just repeated over and over. But that's same for texhno; beat goes on for ages with no change I get bored. Trance too but to a lesser amount as it's more all over the place which I like.
So for me techno isn't the sweet spot and feel few hours I get bored. Do I think its shite? No it's still music. Same with edm, may not be your thing or even hate it but it is still music.
The problem is music is highly subjective and in all genres there are shit tracks and good tracks.
I find people who go bonkers saying xyz is shite and should be destroyed usually are more closed to new music. I really dislike hard rock and metal but understand its music and liked by many.
As for the cross pollution of genres that always happens and can result in new interesting music or crap. There will always be niches for the original "pure" origins if you look.
*these are my opinions and are not to be taken as a absolute truth of the universe and how it is