If you want to be helpful, keep writing both. It's strictly more useful than just writing Celsius. If you decide to do that anyway, don't be too surprised if someone edits your answer later. Same goes for the other way around, of course - I write both units in my answers when I can, despite the fact that I will probably never use Celsius in my kitchen.
We have a lot of American users who unlike you are not terribly familiar with Celsius and will have to keep converting if they don't see Fahrenheit. Your made up 98% number may be right for the world, but not for our site. Forcing some people to convert temperatures isn't going to help anyone out.
Note also that for baking temperatures, no matter how badly you want to use Celsius, in the US your oven will be in Fahrenheit, so Celsius is useless. (Even if it's digital and can do both, everyone will keep theirs in Fahrenheit because that's what all the recipes use.) And even if Celsius were strictly superior and there were few Fahrenheit users here, I'd still be saying this. I don't want this site to start making unnecessary prescriptive rules that make it less useful for some users.
Side note: I notice that you didn't also propose that we enforce metric units of weight and volume. It should be obvious that I think that'd be a bad idea too. Yes, I do like those units, they're easy to convert, providing a concrete benefit in the kitchen (unlike temperature). But all that's only useful if you happen to have a scale and metric measuring cups. The vast majority of Americans will still have to just go convert everything before it's useful. If you can magically convert the entire world to metric, then we can start making these rules. But until then, no reason not to be friendly.