I believe that knowledge is power, and sticking with the point John made, one should be aware that not paying $X in interest, does not mean that $X has all been saved. A bit of math and the true numbers come out. For some, a guaranteed return equal to their mortgage rate is better than the chance to have a higher return. I don't argue that, I'd just expect that one acknowledges the tradeoff.
To your point above, you lose your job. Do you prefer no mortgage, or $100K in bank and some years to go on the loan? That's a tradeoff too, no? You can choose either one, and however you choose is fine for you. There's a groundswell of "mortgages are evil" zealots starting to rear their heads, and many are pushing some math that's questionable, if not simply incorrect.
Keeping all my thoughts to this post, I understand that not everyone rises above the standard deduction. Again, that fact should be part of their decision. I think that it's not over the edge to expect that people be in touch with their situation in this regard; tax bracket, standard or itemized deduction, 401(k)/ IRA details including whether they qualify to deduct IRA or do a Roth. The guy paying 6% on the mortgage, thinking he's 'really' paying 4%, but in fact can't itemize and is in the 15% bracket is not who I am addressing in this forum. But yes, I am sad for such people.
Joe