It's a bit more subtle than that. The sugar is there to make it palatable and addictive. The real problem is it's hyper-processed and ridiculously easy to digest. It'll spike your blood sugar levels then have you wanting more an hour later. There's no point looking at a single food in isolation, you have to look at the entire lifestyle and the kind of lifestyle that includes McDonald's is not a generally a healthy one.

Then again Buffett apparently did it for 6 decades. But he also only had to drive a few minutes to work and probably had a mostly stress free life. You can eat all the healthy veg you want but if your day is punctuated by a dreadful commute and generally filled with stress, that's what will get you.