I don't think it is a matter of "more rights", any more than you get "more rights" when you turn 40 and enter that legally protected class in the US.
The big difference being that you can't stop yourself from aging, you can stop yourself from becoming obese. Short of rare (much more rare than obese folks want you to think) medical conditions, nobody has an excuse to be obese, you're not born that way and you're not naturally inclined to become that way without excessively unhealthy habits.
How people look doesn't really matter to most technical workers, but would you rather hire the ideal-weight handsome person, or the 450 pound ugly guy?
Without a doubt, the ideal-weight handsome guy, because the 450lb obese guy demonstrates simply by being obese he lacks basic self control, and likely doesn't have the discipline I desire from employees. If you look like you can't be bothered to give a damn about your own personal health, why would I expect you to give a damn about your arguably less important job? Not to mention as an employer I don't want the added risk of somebody overworking themselves and having a heart attack on the job, something which seems less likely in an individual who appears healthy.
Yes, employers discriminate, because otherwise they'd be forced to hire every yahoo that strolls in and their business would suffer for it. Some qualities shouldn't be subject to discrimination; ethnicity, sexuality, gender, and plenty more. But obesity? To be obese is, generally speaking, a choice. Most people don't want to accept that, but it's the truth, every day you choose not to start exercising and eating healthy is a day you choose to remain obese. A lot of people argue they don't have time to exercise or the money to eat healthy, but it doesn't take much searching to find helpful advice from folks who thought the same thing until they realized they were completely wrong.
If an employer tells you he's not going to hire you because they maintain a professional workplace and your hair is blue and spikey, you can either choose to do something about your hair or you can throw a fit and act like it's not reasonable to want your employees to give the impression they're employed when people walk in the door and either one is your right. The same with obesity, if somebody tells you your ass won't fit in their chairs so they can't hire you, you can either throw a fit and act like they should invest in all new office furniture to cater to you, or you can go get a bike and invest in your own health, come back and get the job looking (and feeling) like a new person.