The article is pretty thin - they boil it down to social security changes, lack of pensions, and not saving. And two of the reasons that its "impossible" to retire aren't about the possibility to retire, but the desire:
People are living longer and their health is better at older ages.
More people work with their brains rather than brawn.
And those first two (SS and pensions) have nothing to do with early retiring - they're money you get late in life, typically for someone who didn't early retire (or at least with the pension, retired as early as it let them, perhaps, but didn't ER through savings).
If you're going to ER, you probably aren't doing it on Social Security funds. ;) (Though they may be a safety net later, likely you'll have lots of other funds.)
So really their arguments go:
1) People living longer - not as relevant to ER (if you build a stache that should last forever)
2) People work with their brains? Huh? Should give them a reason to ER, to put their brain to good use. Not relevant.
3) Social Security worry #1 - Relevant to retirement; not as relevant to ER
4) Social Security worry #2 - Relevant to retirement; not as relevant to ER
5) Pension Worry - Relevant to retirement; not as relevant to ER
6) Savings down - well yeah, if you don't save, ER isn't possible. But savings sure aren't down for someone trying to ER!
7) Job loss - Relevant to retirement; not as relevant to ER
Really, all of these fears are related to retirement. Someone striving for ER doesn't have to worry as much about a job loss (they're in good financial shape with FU money), don't have to worry about not getting SS (they have other money funding their retirement), don't have to worry as much about living longer, etc..
Trying to ER puts you in BETTER shape to deal with all those things.
Crazy.