"The gig economy works particularly well when it serves to complement full time employment. It provides a way for people to quickly respond to immediate or unplanned economic needs. If people use the gig economy to supplement their income, as a safety net of sorts, they are less likely to be concerned that freelance work lacks the perks of traditional employee-employer relationships like a 401(k). However, this is not the case for full-time freelancers."

So it's for people to pick up extra work, not for people to use as their main job. 

Ideally, yes, but it does not work like this. There are a lot of full-time freelancers as well.  The original article - that I have not yet found - was prompted by a court decision that Uber contractors need to be reclassified as employees - with benefits etc.  Here are a couple more articles on this exact topic:

http://www.huffingtonpost.com/2015/06/17/uber-independent-contractors_n_7604366.html

http://blogs.wsj.com/digits/2015/07/09/do-uber-drivers-really-want-to-be-full-time-employees/