Agreed that the effect is in their head. But that may result in behaviour you may not want in your dojo. Some students may avoid training with disable(s). Some may even leave. The atmosphere of the dojo may (probably will) change.
for better or worse...
I also agree that there is no room for worry on the tatami, for from it. but...when someone is injured and decides to come to practise that person becomes my responsibility. As dojocho I feel I must present problems my students can handle, or just handle. To put them in harms way, deliberately, does not make much sense to me. So when someone is injured I do take that into account because I could be legally liable if somethings happens.
This has happened to one of my first teacher....
I don]t get what putting someone in harms way means. The student is in harms way in a martial art.