Dangerous for whom?
Of course uke is educated to respond differently to 'normal' people, isn't that one of the reasons to practice, so that you are no longer considered 'normal'.
For me, being uke is about offering nage a spirited attack that needs to be dealt with. This can be done at snails pace with a brand new beginner of at full speed with full intent with a weapon. The act of ukemi is to follow through the attack and fully receive nages response. All focus being on maintaining co-ordination throughout. This should result in an escape and a mind to attack again.
What do normal people do, I'm genuinely interested? If you are talking about resisting technique rather than 'following'. Then the normal person is limited in their response, also they can't use resistance against someone who is 'non-resistant'
I can't see the you tube links offered above (at work, yt blocked). For me some of the worst ukemi I see on the net, are ukes who give a good 'strong' grab, who have their balance taken easily (hopping on one leg etc) and are easily dealt with. They have too much tension in the system to stay fully co-ordinated.
The hardest (and paradoxically the easiest) uke to throw is one who keeps his centre in his hands, does not resist nage's technique, but rather follows it through to its logical conclusion, remaining fully co-ordinated and balanced all the time. The result is either a nice clean throw, beacuse the technique was correct, or as is often the case, the technique stops because nage has tried to throw/lock/manhandle uke while not following the principles of aikido.
I forget what the world of normal is like sometimes
I don't know if anyone else has experienced this but when I train in dojo with "highly responsive" ukemi uke ends up in a heap on the mat. My dojo doesn't do the "highly responsive" thing and our Aikido is about using a relaxed body more than taisabaki and when we train with "responsive" people they get hurt.
As I see it they're not actually responsive; they actually make the technique for tori so when someone actually does a technique on them it's a totally new experience and you are literally throwing a total beginner who might be nidan or sandan.
That's if you can throw them. Many of them will make the attack and then start running immediately and all you can do is move to keep up with them, then for no reason to do with you their legs suddenly fly up from under them and they fall over. I've lost patience with people and "thrown" them with one finger pressed lightly on the nape of their neck and been congratulated for it. Anything will work with a responsive uke, you can take your hand out of your centre and throw them with a flick of your wrist.
The same goes for techniques: I tend to find that the guys that do train in a "responsive" way can't actually move anyone who chooses not to respond. By this I don't mean go tense or resist I mean someone who just stands there relaxed. Also I tend to think that if I'm moving around in such a way that I can choose to counter I may as well not move in the first place or I may as well counter them. In not doing so I'm hiding an important fact from them; my posture isn't broken and neither is my balance.