That's not the claim GP made. They said their coworkers spent an amount of money that seemed crazy to the GP. There's nothing to refute! Repliers don't know the coworkers. They can't refute GP's personal metrics. And we already know that some people don't think spending money on coffee is ok, because GP's co-workers are doing it every week.
Of course there is something to refute - with the provided info we can only assume that GP is referring to the co-workers spending 3-5 dollars per coffee at a coffee shop. The replies are providing an alternative to this method of consumption.
So? The GP is still allowed to think it's crazy that those people spend that amount of money. The GP is surely aware, like everyone is, that you can make food for less than you can buy premade stuff for. As are the people buying coffee at the coffee shop, who will go on spending it no matter how many people reply to his comment.
So unless people are trying to get the GP to join in their addiction (but cheaper!), there's no point in telling him all this. Nothing is being refuted.
