The main flaw in the "logic" of thinking Ripple is a scam is on the one hand claiming that they are going to get rich off XRP but then saying that Ripple is useless and only exists to defraud the public. It should be obvious that these are mutually exclusive possibilities.
First of all, these are obviously not mutually exclusive. I think they are TRYING to get extremely rich, but they are FAILING to achieve that and ripple will not be succesful.
I also think that you are purposefully creating a strawman by introducing words like 'scam' and 'defraud' into the conversation. I have not heard many people opposing ripple using any words like that and the proponents of ripple on the other hand are trying to polarize the discussion and drive it to the gutter by trying to get the discussion to go overboard and then accuse the discussion not making make any sense.
The problem with ripple is just that it does not look like a good idea.
Ripple could be superior to Bitcoin in so many ways.Near instant confirmations, no problems with micro-transactions, no wasted resources going to mining, and no way to rewrite history via 51% style attacks.
Fiat money has some qualities over bitcoin where fiat money is superior and these are all such qualities. However bitcoin people have decided that bitcoin has qualities over fiat money where bitcoin is superior and those weigh much more in comparison. Ripple on the other hand craps all over the bitcoin philosophy in so many issues. Preaching ripple and qualities of ripple sounds in most cases like telling bitcoin people that they have got it all wrong and the bitcoin philosophy sucks and ripple philosophy that is 180 degrees opposite to bitcoin philosophy is superior and bitcoin people have got it all wrong. I don't understand what the ripple people think they are going to achieve by first shouting out such a message and then when they see that many bitcoin people are not instantly making the 180 degree turn in their thinking, they turn into accusing bitcoin people to be stupid and start calling them names.