I doubt that
WoTC will lose very much money from downloading of the core books.
In my opinion, a publisher is much less likely to lose a sale to a PDF when the material in question is going to be used again and again. And we're talking about the core books here, the books that get used the most.
Where they may lose money is in PDF sales. I own quite a few
WoTC PDFs and the DRM on them makes them much more difficult to read for some reason -- I have a couple where my computer freezes up for 10 seconds every time I try to page them. I have sent emails to DriveThruRPG customer service about this issue, but to my knowledge it hasn't been resolved. If in the future I am faced with the choice of a download that is easy to use, or a bought PDF that is a nightmare, that fact will not work to
WOTC's advantage.
As far as downloading being illegal, well it is a matter of civil law, not criminal law, in the USA. In some other jurisdictions it's completely legal.
And as for the morality.. well, I would say that the people who develop RPGs deserve to be paid. If you download a copy of a
WOTC publication, and you haven't bought the physical copy as well, you aren't doing your part to provide for those who make our hobby possible.
Ken