An basic HR principle states that employees should get paid according to their responsibilities. If have a lot of responsibilities or the ones you have are particularly demanding, you should get paid accordingly. Flight attendants do have to deal with a lot of issues regularly that can be dynamic, think of their feet, train extensively (or at least they should), and there are certain, and potentially lethal, risks involved. That all added together should be rewarded with significant pay along with decent benefits. Whether or not that is worth $100,000 I am not sure, but that is not really my place to judge (I am not an HR manager). United Airlines seems to think they are worth that so who am I to judge? I believe it sounds within reason considering their responsibilities.
Just like Pilots, flight attendants have a lot of responsibility on an airplane.. They have to be aware of what is going on, on the plane and handle any passenger disputes. They have to deal with people when they are not at their best. Normal people who normally don't lash out, may be on edge because they don't enjoy flying. Flight Attendants have to deal with that as well as making sure everyone is safe and ad-hearing to the guidelines their bosses have set in place. They are also constantly traveling which takes them away from their families or in some cases they don't have a family of their own because of their job and they should be compensated for that.
In offer senior flight attendants $100,000 to leave the company United is under valuing their job. $100,000 is less than 2-1/2 years pay for the average flight attendant. The buyout offer is an attempt to reduce the company's flight attendant headcount without layoffs. But is they truly want it to succeed they to offer a buyout that is a fair reflection of the flight attendant's income.
No I do not think that the salary of a flight attendant is too high. Flight attendants have a fairly hard shop attending to customers. Not to mention they are in a significant amount of danger by being in an airplane that can possibly crash all of the time. They are also gone from their families most of the time.
I don't think that flight attendants are paid too much. There are actually many professions that pay out large sums of money to those that are employed in those certain fields. Many of those professions are not nearly as dangerous as the job of a flight attendant. In my opinion, if you can get more money for doing a certain job, then that is more than okay.