Yes, you are scaring yourself away from tampons- and no, you don't have reason to fear your body rejecting them of its own accord. ;) Like roaring_woman said, if you put the tampon too far down it will be uncomfortable (that's why applicators are convenient), and if you put it too far down while you're dry, it will chafe doubly. If you insert it correctly, at the right angle, with trimmed nails, while relaxed, it will not hurt. But then, I'm sure the same goes for the Divacup.

I've been using tampons for ten years and there's nothing wrong with me, in fact I'm quite healthy, and tampons do not "give" me cramps. Once I figured out how to use them and got over my paranoia about this and that, it was fine. I don't even count the hours anymore, I know when they need to be taken out, and I never stain my underwear with leaks. I also wear them at night, and in conjunction with pads of varying thickness.

If you want to use tampons, and approach them calmly with a willingness to use them correctly, you will not have any problems. That being said, it seems like you're pretty sold on the Divacup, so good luck with that. Bless!