Commercial parody is commonplace fair use. If it surpasses the original... oh well.

The amount being used becomes negligible as the corpus grows. Filtering a billion webpages into one gigabyte means their average contribution is one byte. Play with the numbers all you like, it's gonna come out to less than a paragraph.

If we went full copyright maximalist, and criminally banned using anything but public-domain / BSD / CC0 works, the commercial impact would not be much different. The technology itself shifts the economics of text, images, video, and code.