...suddenly politically wrong, a crime, a huge sin?

Like literally if I notice one of my friends getting fat I'll tell them "hey, you're getting fat" and they won't get hurt because it's the truth.

It's strange that calling a fat person "fat" for Americans is suddenly as offensive as a white person call a black one "n****".
Of course it is wrong to call someone fat if your intention is to bully or to discriminate others. But what if you only want to describe a person like "hey, have you seen my friend? He's white, fat, hairy and sweaty?", what's wrong with that?

I'm sure there are nicer ways to get to your point

common sense lol

It's an ugly/nasty word, but the English language doesn't really have many similar/better words you can use.

Most of the time it's said in a negative/insulting way.

It's generally mean to point out somebody's flaws* in such a straight forward way. You either find an indirect way to say it or you don't say anything at all. Slightly hypocritical, of course, but it's part of society's foundation. We'd be a jungle if everyone was that blunt.

*going by social stereotype, not personal opinion

That's right. In Italian you can say it in many elegant ways. "Ti vedo in carne", "che pinguedine", "come sei adiposo ultimamente"... but if we want to insult we can just say brutto ciccione di merda.

Because it is

Omg hey lovely, long time no see

you can say it in a much nicer manner, and should only really if the person is gaining alot fast, or is basically very overweight in a health matter

Really? Like even using the word "chubby", "thick" are also offensive now?

@ me next time

Thick/thicc is like exclusively used positively and is thus interpreted as such

OMG that's not what I meant. I edited the op.

Everyone can tell a skinny person "omg your SOOOO skinny!!1" without them getting offended but thats because people use it in a positive way whereas being fat has too many negative connotations

oh, okay. Thanks.

your friend knows she's getting fat, she doesn't need you to save her

your poor friends

If you need to use their weight as a descriptor, plus sized, thick, heavy-set, full figured" are terms I've used interchangeably which don't carry such a harsh connotation as "fat, obese, overweight" etc. Will they sometimes be a little awkward? Yes, but it's part of being a decent person & having friends.