The problem with this line of argument is how do you calculate the probabilty of mutation and natural selection forming a given biological system? In the case of the coins, it's easy to calculate the probabilty of a given sequence of coins. However, natural selection provides a non-random input to biological systems. In your analogy, this would be akin to replacing some number of nickels with two-headed ones. If we replaced, for example, 950 of the 1000 nickels with two headed ones, is it still more reasonable to conclude that the pile is a result of design? How about replacing 990 of them? At what point do you draw the line?
However, the real problem with your whole argument is really that you consider some equally probable events to be more improbable than others. Which events are considered more improbable? Namely, those that result in a recognizable pattern. Humans are good at pattern recognition. The problem is that we are so good at it that we recognize patterns where none really exist. Just for another example, if you play the Powerball lottery, I'll bet you've never played a ticket with the numbers 1,2,3,4,5 and a powerball of 6. If not, why not? That ticket is equally unlikely to win as any other. Just intuitively, we consider such recognizable patterns as unlikely to happen randomly. However, given enough drawings of the Powerball, it becomes likely that this set of numbers will indeed be drawn.
Similarly, I once had a statistics professor assign a class the task of flipping a coin 10000 times and recording the results. Inevitably, some people didn't actually flip the coin and just made up results. Just as inevitably, the prof could always tell who faked it and who really did it. How could he do this? In a series of 10000 coin flips it's almost inevitable that there should be some sequence of 6 or 7 heads in a row. It's also human nature that if you were trying to fake such a random sequence, you would NOT put 6 or 7 heads in a row in the sequence because you would consider this unlikely to happen.
The point is that arguments based on improbabilty are weak ones. Very frequently, we have no real basis for calculating the probability in the first place. Even if we do, we have little basis for saying that a particular configuration for a biological system is any more unlikely to have happened by stochiastic processes than any other configuration for that system. If that's the best that ID can do, then biology will undoubtedly never take it seriously. It's akin to stating that the Powerball drawing must be fixed because the numbers drawn were 1,2,3,4 and 5 with a Powerball of 6, and this is exceptionally unlikely to have happened without fixing the drawing.
The issue is not how weak or strong it is but how legitimate it is.
Very frequently, we have no real basis for calculating the probability in the first place. Even if we do, we have little basis for saying that a particular configuration for a biological system is any more unlikely to have happened by stochiastic processes than any other configuration for that system. If that's the best that ID can do, then biology will undoubtedly never take it seriously. It's akin to stating that the Powerball drawing must be fixed because the numbers drawn were 1,2,3,4 and 5 with a Powerball of 6, and this is exceptionally unlikely to have happened without fixing the drawing.
It's akin to suspecting that the Powerball drawing might have been fixed because the numbes drawn were 1,2,3,4 and 5 with a Powerball of 6. Perhaps it was random, but if it wasn't there might be evidence of tampering. And if the Powerball people fought an investigation of that unusual drawing tooth and nail rather than cooperating with it, do you think that would convince people that it was a legitimate random drawing or do you think it would make them think the Powerball people have something to hide?