You just assumed that fat people would want to pay more for being fat and call them a hypocrite if they don't want to pay more
Hold on, you're saying I'm assuming that they won't want to pay more, and I'm also assuming that they will want to pay more?! Make up your mind! Either way though I'm making no assumptions about fat people's preferences over being charged a fair amount. As for the hypocrisy, you appear to be using your selective memory again. Hypocrisy is typically where you say A but do B. That doesn't mean that saying A by itself is hypocritical, just as doing B by itself is hypocritical. Read back and you should be able to find the 'B' to go with the 'A'.
Healthcare they will likely need is determined by their illnesses. These illnesses are usually issues the older they get. So would it not also be true that age plays a factor? As people get older the more healthcare they need. For example at 21 I did not need any healthcare. But now that I am into 50’s I need more healthcare. So you are paying for my age related illnesses. We should then by your logic have and age tax or stop treating people over 40 because that is the tipping point.
Well you can't choose to grow old, or get younger again, so for a universal healthcare system that would raise obvious moral issues, especially when you factor in that many old people who have retired will be on a lower income and hence wouldn't be able to pay any such tax as easily, and UHC will be funded by taxation which itself is based on ability to pay.
In a (private) insurance system however it makes every sense to allow companies to charge based on age. Companies are afterall profit making, and to prevent them charging on age could effectively mean they end up having to provide insurance to the elderly at a loss, and/or refusing to provide insurance for that reason, and/or heavily overcharging the young if they have to provide insurance to the elderly and can't charge more.
You're using those points to justify making someone else's healthcare your business
Actually I'm effectively using those points to justify no longer making someone else's healthcare my business with an insurance system, since a fat surcharge would mean I'd no longer be subsidising fat people and hence it wouldn't be my business. Without allowing any such surcharge though I'm going to lose out based on other people's healthcare and hence I'll take more of an interest in it (such as supporting government programmes to restrict peoples ability to choose to be fat). With the tax/surcharge, I shouldn't care whether people choose to get fat or not because it won't affect me.