Just because there are business reasons for making SaaS webapps doesn't change the fact that they do in fact collect private information -- and that brings with it all the potential for abuse, leaks, sale of the information without my consent, tracking, spying, etc.
Call it what you will, but I certainly don't want my private information in the hands of some person or entity I don't trust.
As for who cares what jobs I apply to, you might not have noticed but there's something called datamining that can link all sorts of innocuous-seeming information to draw conclusions with serious privacy implications.
For example, before some researchers actually went ahead and did this, who would have guessed that your Netflix viewing habits could be used to determine your political preferences or sexual orientation? And would you really want Netflix and anyone who they sell the information to or anyone who manages to hack their servers knowing these?
You might not mind, but I bet a lot of other people do. Unfortunately, plenty of Netflix users probably still don't know that this kind of abuse -- and it is abuse -- is possible.
Something else that was in the news about a year ago or so is the recent trend of companies trolling through Facebook to see who your friends are, and determine from that whether they think you're credit-worth (or worthy of employment). Again, something apparently innocuous being subverted to have serious unintended consequences for the victims who were naive enough to give out their private information.
There are hundreds of examples like these -- there have been many books and articles written about the trend towards a surveillance society and the loss of privacy that's overcoming our world, with the advent of highly sophisticated technologies and the internet.
SaaS sites and the invasion of privacy that they encourage and participate in are a big part of this problem.