A random scraper, on the other hand, just racks up my AWS bill and contributes nothing in return. You'd have to be very, very convincing in your bot description (yes, I do check out the link in the user-agent string to see what the bot claims to be for) in order to justify using other people's resources on a large scale and not giving anything back.
An open web that is accessible to all sounds great, but that ideal only holds between consenting adults. Not parasites.