If you weigh 70 kg and want to take with you 73 kg of luggage, you have to pay a massive amount in addition to your normal fare. If you weigh 120 kg you still get a free allowance of 23 kg of luggage. How can this be fair? Perhaps we should go back to the early days of civil aviation when everyone was weighed at Croydon aerodrome before being allowed to board. In those days I think it was to do with fuelling, but it could now be used for charging purposes.
Airlines do require very large people to pay for two seats if one isn't wide enough, or upgrade to a higher class with more 'bumroom'.