I discover many books I love on the wild web, and then decide to get the paper version when I'm hooked by the style / want to read it while doing digital detox / want to be able to leaf through efficiently if it is a technical book, etc.

If anything, wild ebooks have increased a lot my paper books purchases, and even if not everybody is like that, even for the percent that is alike it would mean that more free ebooks means more purchases.