Response: We have never found this to be the case. Bike helmets do not affect vision. If the helmet intrudes on upward vision it will be evident to the user, who can adjust the tilt of the helmet to raise the front lip. Bike helmets also do not affect hearing, since normally they do not cover the ears. That question is easily settled by riding with and without a helmet, or by standing beside a road with helmet on and off. The US DOT has conducted a study on this question using motorcycle helmets and found that even these larger helmets with additional coverage do not affect hearing, and have little effect on vision.
Helmets are heavy, hot and uncomfortable.
Response: This is a subjective judgment for each individual, and is easily tested by the user. Most riders find today's helmets light, comfortable and cool enough.