You are paying £5 for the cost of food, the cost of employees, the cost of the premises and various other bits and bobs. Especially if you are sitting down to eat you need to factor in the cost of you hogging their tables/chairs as well.
It is more than likely that your £200 dinner costs only a little more than your McD food as in the actual food ingredients. Given this premium, which you are paying for SERVICE&AMBIENCE (hint:hint), you are not expected to rush to the kitchen and wash up.
Also, the Ronald McDs finest are people like you and me, who work at a crappy job to make ends meet for various reasons, least being that they are too "dumb" to be worthy of anything better (as many people seem to think). The work conditions and pressure at fast food outlets is very high for very little wage and no prospects, with the threat of getting sacked hanging over your head over the smallest incident. If you have a bin within sort walking distance and your food consists of cardboard and wrappers (a.k.a no washing up), the least courteous and decent thing to do is to bin it yourself. It doesn't cost you anything, it's no burden to you and it saves the people who work there a bit of time to serve the next customer faster - who may be yourself next time.
The kind of attitude described in your post is disheartening to say the least. Disheartening, but not surprising.