Um Mel, maybe you should do some reading online before you say keeping goldfish in a heated tank is not a good thing and that we are giving bad advice, I have heard of a lot of people keeping them successfully in tanks with temps upto 28c, most tropical tanks will be around 24c which is no more than your pond heats up to on a hot summer day.
Your goldfish were probably stressed and gasping for air because you didn't cycle the tank and didn't put enough oxygen in there with them, nothing to do with temp, did you think of that?
Maybe next time you want to say that someone's advice is wrong you might want to back up your theory with some facts or evidence.