Because our culture has become desensitized to any aesthetic qualities which are now deemed to be 'less than ideal'. As well, balding represents a lack of youthfulness, exuberance, and a lack of alpha-masculinity. The hair falling out symbolizes (ironically) a lack of ideal 'maleness'. Baldness and balding is often conflated with weakness and atypical genetic traits.
I hear ya on this and it seems that you think the public's negative opinion of bald people isn't a well-founded one at all!
The aesthetic part I can give them mainly because there are many people who use the comb-over, hair-plugs, etc. techniques that truly do look bad.. but I think bald guys are typically astute, confident, sharp looking men who are generally well kept!
I find the balding = inferior masculinity ironic just as much.. are older men (correlated to balding) typically just as virile and sexually productive as younger men? I'm not sure where this miconception thing came but it seems to have been stuck in a lot of heads..
I also see the supposed link between baldness and a weakness in genetics -- that the baldness is like a warning sign that a man's genes are of inferior quality? I have read a study that bald men have a slightly elevated risk of heart-related problems but beyond that, is there really a substantial link? I dont think so -- I think your claim is correct that the majority of people have been conditioned to ridicule anything that isn't aesthetic perfection.
Additionally, this drive to ridicule might lead to unfounded or mythical claims that really have no scientific basis yes?