Taken to its logical extreme, the decision to always buy goods from the cheapest source will inevitably eliminate players from any market. This is why businesses don't compete on price alone; they also advertise and offer promotions. So I agree that some attention must be paid to the consequences of one's choices (whether these be moral or otherwise). I'm no market fundamentalist.
But what I don't like is the suggestion that if you source one particular ingredient from abroad, you are thereby guilty of failing to support indigenous businesses. I for one use the HBC all the time. In fact I spend quite a lot of my money there (just ask my girlfriend!). I have met some of the people who work in Mountmellick and I like them a lot. It's a fantastic business. The reality is that the odd bulk purchase from abroad hurts nobody in Ireland. In fact, it may help them. With all this grain to be brewed, I'll need to source auxiliary supplies (yeast, hops, extract, sanitizing solution etc.). And I'm pretty certain that the HBC will be top of my list.