I’ve just been through this particular mill and I’m with you, OP.
I’d never heard of hysteroscopy when I was referred for one so like you, I did my research. Some of the stories online are horrific! And the minute I saw that there’s actually an organised ‘Campaign for pain-free hysteroscopy’, that was enough to set my alarm bells ringing.
What you can do is, when they give you the consent form, you can consent only to the investigative part of the procedure to be done at that initial appointment. There’s a separate part of the form to sign to give consent for treatment (eg removal of polyps or fibroids) which is usually done at the same time, on what they call a ‘see and treat’ basis - so without any pain relief. I wasn’t prepared to consent to that in advance and I told them so. They weren’t happy about it and rolled their eyes a lot, and made lots of doom & gloom pronouncements but I stuck to my guns.
You can also request that they do as much as possible of the procedure without using a speculum. They don’t actually need one to get the camera up there, and again although they’ll moan, they can even take a biopsy of the womb lining this way. I had a slight advantage in this case because it was already in my notes that I find speculum examination painful (due to menopause), but basically you can tell them to stop the hysteroscopy at any point if you’re finding it too painful, and request to have it completed under GA. I’ve just had this done for a polypectomy this week and although I was petrified, it was preferable to the alternative.
But I agree with you, I can’t understand why it’s one extreme or the other. It’s scarcely a choice, is it? - have a full-on operation (which I’m phobic about) or endure medieval barbarism where they may as well just tell you to bite down on a stick, for all the good taking a couple of paracetamol before the procedure will do! 
It might be worth researching all the hospitals in your area, as a small number have revised their practices in the face of campaigning, and do now actually offer gas & air or an epidural for this procedure. I found this out too late, after I’d picked the wrong hospital from the list they offered me (this might only happen if you’re on the fast track though).