Charity has its limits

Oh dear. Kenodoxia has now been cited in Mary Beard's 'Don's diary' (in the latest Cam magazine) as a vaguely scholarly trip along the by-ways of ancient philosophy. I have a sneaking feeling I haven't been very scholarly lately, nor very philosophical. But here's a gesture in that direction.

What's the worst argument to be found in an ancient philosophical text? I mean the argument that is the most obviously fallacious or otherwise glaringly misguided? Now, the Principle of Charity often leads us in the business to try to do the best for whatever apparently ghastly bit of reasoning we might find. (Think, for example, of the 'Argument from opposites' in Plato's Phaedo: 'being dead' and 'being alive' are opposites in the required sense, are they Socrates?)

But I can't do very much for the following:

'If you are light, pain, I can bear you; if I cannot bear you, you are short.'

levis es si ferre possum; brevis es si ferre non possum.

Sen. Ep. Mor. 24.14

This is meant to persuade us that intense pain does not last. It's not just Seneca who peddles this rubbish, though: he probably caught it from an Epicurean (see Epic. Ep. Men. 133; KD 4; SV 4; Diog. Oin. fr. 42 Smith; also Cic. Tusc. 2.44.) But Seneca is daft enough to repeat it, even thanking nature for making it so (Ep. Mor. 78.7). If it's an argument at all and not just a daftly optimistic assertion, then it must mean something like this:

If pain is intolerable then it will kill you; it will not last. If pain lasts then it must therefore be tolerable.

This is of course true only in a very special and literal sense of 'intolerable'. I doubt anyone will be much relieved when they turn to a doctor and complain of excruciating agony if the doctor turns round and says: 'Well, it hasn't killed you. So it must be tolerable. Luck you.' Anyone persuaded by this not to worry about pain is an idiot or (and?) already, like Seneca, a Stoic...

Any arguments worse than this?