Something I found compelling was an analogy posted in the comments by a reader. The following is the quote:
Taking without contributing at all is destructive. My local bank branch is 5 mins walk away. It has free coffee for customers. I am a customer. What happens if I no longer buy coffee at home but get all my coffee from the bank? What if I go a step further and sell the bank's coffee in my coffee shop? Most likely, this will mean no more free coffee in the bank, for anyone. By your logic I didn't do anything wrong. BUT I HAVE PRODUCED A BAD OUTCOME "Everything free" might be a noble aim but how can it work in practice? You fail to consider the practical implications of "take with no give."
While this analogy seems good, it kinda misses the mark slightly. The bank's business model is based on the financial services it provides. The coffee is just a small perk to keep you happy while you are there using the bank's financial services. So the analogy doesn't isn't 100% stable, though I still see the author's point. If you are a consumer of open source and you contribute back in absolutely no way, then the community is said to be at risk. Remember, contributing is as easy as participating in mailing list discussions and filing bugs. That's exactly how I tend to get started with any open source project because the bar for participation is usually pretty low.
Anyway, it's an interesting topic for sure as I've had many of these types of discussions over the years at software conferences, on consulting gigs and even inside the companies where I have worked. What's interesting is very wide range of the points in such a discussion. But I digress...