That's a fair point. Every author has the right to look after his own interests, and there are multiple publishers out there.
A close look is definitely needed at the terms and conditions (including copyrights, royalty percentage and advance).

That said, I should think that printing a lot of worthless books would actually degrade a publisher's portfolio, and damage their long-term reputation. Therefore no publisher can afford to be careless about the content OR quality of their books.

Secondly, the risk of loss comes from the UNSOLD books.
Any printer has a minimum printing quantity (or the price shoots up).
Once printed, he has to stock these books globally, and spend after logistics (for global delivery).
Only the e-book versions have no such costs.

Finally, the idea of a spam is relative: Suppose we get a mail from McGraw Hill? Will that still be spam? :)

-Narayan