This is world of consumerism as some economists say "The more you consume the more you pay".So a person with higher weight is obliged to pay more.When one has extra luggage don't they pay more this is similar to it.Also this guideline may incite a feeling of greater health consciousness among the population.
This is no where near illegal.
The reason that airplane companies do this is because it actually costs more to fly someone who weighs more. It takes more fuel in the plane to fly if a person on board is overweight. If i buy a ticket at 140 pounds and another person buy a ticket at 300 pounds it wold simply be an injustice for those to costs the same. I wold be paying the same amount of money even though i cost less to fly.
Take this to a more bigger picture.
Airline companies, if not allowed to charge by weight, will have to raise each individual ticket price to cover the extra cost of fuel. A person who is not overweight would then actually be paying for a person to be overweight which is highly unfair.I should not have to pay for a person to fly if he is overweight, that should come out of his pocket.
This is not discrimination.
Discrimination would be refusing to serve the person.
If the airline said they didnt like fat people so they arnt going to serve them, then yea thats discrimination and illegal. The discrimination act was made to protect people who are do not effect the business, such as a person who is black, however, weight does effect the airline companies.
Since weight is a controllable aspect of a persons life, then their choice, is harming the company. Which is wrong on their part. If a person is simply lazy, then the airline should not be responsible for his weight. If he simply loves food, the airline should not have to pay for his lack of restraint. Of course some people can not control it due to disorders or diseases beyond their control, but that is a fraction of a fraction of the people who can be put into the category of being overweight.
Charging by wieght is completly Just
In my thoughts this is illegal due to a number of different laws that are incorporated with customers.
For example - Discrimationary act - isn't this discriminating customers to their size when flying!!
Human Rights Act: Isn't this a case of not treating people fairly!! The human rights act states that all people should be treated fairly and equally
Privacy Act: isn't this against the privacy act as it is effecting peoples privacy by asking them how much they weigh at airport and being charged accordingly. Some people may feel self conscious about their weight and don't want others to know of it