I worked for McDonalds for 6 years and I was a manager there, some of the things people try to tell me about it is rubbish.
There is a very strict Food Safety guide that has to be followed at all times. There are also many SOR's (like an audit/inspection) performed by head office, we have audits from health inspectors and pest control places quite regularly.
At the end of the day people believe what they want.
No Macca's isn't the healthiest food, if you have a problem with that then simply don't eat it?