Maybe you should stop and think about that for a second.
Here's a little experiment for you to try- First find a helmet that someone was wearing during a crash, put it on, and have someone smack a beer bottle into the side of your head. Then try it with no helmet at all. According to your comment, you should feel no difference at all, since the helmet that took a crash is now "useless".
Yes, most ski helmets are "single impact". Because generally a good impact will crush, crack, or otherwise comprimise the integrity of the foam (usually in a specific spot). And then it will not be as strong as when it was new, and yes, it would be nice to replace it with a shiny brand new one.
But to say that it is "useless" or "pointless" now? Do you really believe that because it's taken an impact, it will now do absolutely nothing?
Are you saying that if you were to take an impact to the head, you might as well not wear a helmet that has taken a crash before, because now all of that foam and plastic that surrounds your head no longer obeys the laws of physics, and it will feel just like hitting your bare skull on ice?
Don't take this the wrong way, it is a great idea to replace your helmet after a big hit, especially if the foam is cracked.
But give the guy a break, it is certainly not "useless" to wear a helmet that has taken a hit, when compared to no helmet. In fact even wearing a helmet that is fully cracked through in 5 places is still going to protect your head about 500% more than no helmet at all, it just won't be as good as a new one (not a good idea, just making the point).
Listen to the laws of physics, instead of the manufacturers who would like you to buy 10 helmets per season. Inspect your helmet after a big crash, and replace it if anything is cracked or feels "soft".