"If the internet stopped people from falling for bullshit, "post-truth" would not have been 'word of the year' for 2016."
which is making a general claim. Whereas now you're implying that you weren't making a general claim about "stopped".
If you 'stop' corruption, it doesn't mean you 100% eliminate corruption. A journalist can 'stop people in the street' to talk to them, but that doesn't mean that they stand still rather that walk-and-talk. If a parent is able to 'stop' a kid sleeping badly, it doesn't mean their kid never again sleeps badly, just that the incidence is considerably reduced. Even a traffic 'stop' sign doesn't completely stop people all the time. 'Stop', when applied to human behaviour, is not the fucking same as corking a bloody wine bottle.
Let me put it another way: in your subsequent replies you are implying that what your original claim meant was "If the internet stopped even just a few people from falling for bullshit, "post-truth" would not have been 'word of the year' for 2016." which is clearly not what you meant (and, BTW, would clearly be a false statement) - hence the equivocation.
the person you're replying to didn't make such a strong claim.