That may be the case in the UK but in the US some fast food chains use different suppliers depending on their location, and even if they use the same supplier the raw ingredients may come from somewhere else and be processed in a different factory.
I hate to bust your bubble, but I actually worked in several different McDs, one of them in Germany, one of them in the States. It's the same everywhere. The burgers are made differently, some with thick tomatoes, some with thin, some grilled, some fried, but in the end, what you eat is all the same. If you took the buns of McD, Burger King, Wendy's and Sonic, and made a chemical analysis, the results would be exactly the same. So if you say that McD's burgers taste 'chemical' to you, and the others don't, then it's only because the others put more spices on it (or thicker slices of tomato) to make it taste more natural.
I'm not defending any fast food chain, despite working at McD's, all I'm saying is that there is none of them better than the others.
As for the hygiene thing, as Mali pointed out, that can happen everywhere, fast food restaurant or not. Plus, when I worked as a branch manager at a McD in Germany, it was absolutely drilled into us that hygiene was important. Everybody had to wear hair nets, even the guys, and if you touched any food or machinery without gloves, you were out on your backside faster than you could say 'Chicken McNugget'. I personally fired three people for not complying with hygiene standards.
Now, it's a few years since I worked there, so things have either deteriorated a lot since then, or it is something that is different depending on where you are. Maybe standards in the US are different. I noticed that here in the UK they seem to be, and I have walked out of a McDonalds because the place was simply a mess. That said, the other week hubby sent me to KFC (I can't eat anything they make, they are using a spice that makes me nauseous to the highest degree), and I ended up leaving without food because I had watched the dude packing the stuff into the boxes stand there and scratch at his pimples, then touch the food.
All of that said....I know how bad things can be, and I still like my fast food. I don't do Burger King cause the grilled stuff doesn't agree with my stomach, and I don't do KFC because of the spice, but everything else is fine with me. I know it's bad, and I know it's all chemicals and that stuff....but has anybody ever developed any weird disease from having the occasional burger? Grew an extra set of testicles after having a BigMac? Developed a third boob because of a Whopper? Nope. The only thing I developed from eating fast food is a fat behind, and that is my fault, not theirs. They didn't force me to eat their stuff, did they? I don't see anything wrong with fast food (no matter which particular chain it comes from), as long as it is in moderation....like everything else.
And you know what? I'd kill for a McChicken sandwich right now.....