Originally Posted by KVS
There can, potentially, be value to some (but not all) cardholders. For example, this mechanism allows the person to immediately know exactly how much they have spent in their 'home' currency as opposed to them having to wait for their statement to arrive to discover that amount.
Total BS. In these days where the amount is available with a couple of mouse clicks from the nearest internet cafe and the charges appear almost immediately, knowing how much more additional money you are paying the merchant has no value except in some 0.00001% of the cases where you are running close to the limit and want the exact amount to the nearest tens of dollars or so. Seems like a totally BS scheme thought up by a bean-counter educated in the school of PT Barnum.
They don't really play any special role in this kind of an arrangement.
Of course, if this practice discourages credit card use even in a small portion of their customers who are confused about the high charges for use of their credit card, then they will be vested in preventing the proliferation of this. On the other hand if they have their hands in the pie as well, then they may not be inclined to do anything about it. So it is good to know where they stand.
Of course, a pointless battle is going to be far more beneficial than my solid advice that works
today 
...
Actualy, they aren't mutually exclusive.
Your advice works for a few of those who realize this scam and can certainly be used while fighting the battle to ensure that millions of others aren't defrauded before everyone wises up. Clearly this scam is counting on many people not noticing which is why it seems hypocracy to claim that people should just be careful.
You might have chosen the wrong battlefield for your battle
.
As Steve mentioned above, the bad PR might be a bigger problem to merchants than the legality of it. So we will see. Nothing has been gained in history by naysayers.