'The psycological difference of not having 4 or 5 mm of plexiglass was very real. It was never enough to stop me aerobatting but the feeling was very much there'.
In the pre huggy-fluffy days, vertical metal ladders on the outside of buildings and towers were fitted with metal hoops to give the same feeling of security. Not allowed to climb them nowadays of course without multiple ropes and safety nets.
I seem to remember, as a space cadet, before a trip in a Sioux at Ternhill many moons ago, that the yellow line painted around the bubble canopy was there to prevent similar feelings of insecurity.