A classic example of bad math:
"unrestrained population increases geometrically;
 food production increases arithmetically.
 The only check on growth is death and famine;
 hence Utopians will create death and famine!"

Critique:
- fancy language // math as rhetorical tool
- math is just wrong: food increases geometrically, and much faster
  too!
- there's other checks on growth: don't have so many kids!
  (growth is actually logistic)
- he's lying.
- rigorous reasoning from faulty premises
These were all obvious at the time, to anyone who cared/thought.

...
danger of bad premises
politics underlying argument:
 - colonialism/expansion
 - anti-poor, anti-liberal agenda
 - specifically, anti-Utopian, anti-"bettering the world"

Great (scathing!) critiques by William Hazlitt are:
"Malthus"
  (a character sketch)
"An Examination of Mr. Malthus's Doctrines"
  an examination of the claims
"On the Originality of Mr Malthus's Essay"
  a long citation from Wallace
  Wallace (a mid-18th century Scot, not Darwin's contemporary):
  "Various Prospects of Mankind, Nature, and Providence"
  ...showing Malthus's source
in "Political Essays, with Sketches of Public Characters"

quote:
"The principle laid down by this author, that population could not go
on for ever increasing at its natural rate, or free from every
restraint, either moral or physical, without ultimately outstripping
the utmost possible increase of the means of subsistence, we hold to
be unquestionable, if not self-evident: the other principle assumed by
the original author, viz. that vice and misery are the only possible
checks to population, we hold to be false as a matter of fact, and
peculiarly absurd and contradictory, when applied to that state of
society contemplated by the author, that is to say, one in which
abstract reason and pure virtue, or a regard to the general good,
should have got the better of every animal instinct and selfish
passion."

gloss: see the rhetoric in Malthus: take an obvious statement and a
  falsehood, and cleave them, then proceed.

"...his mathematics are altogether spurious. Entirely groundless as
they are, they have still been of the greatest use for Mr Malthus, in
alarming the imagination and confounding the understanding of his
readers."

gloss: math as rhetorical tool