This is a disingenuous and overly-glib argument. There are numerous obvious differences:
1. We can enforce the law on Facebook in ways we can't with completely agnostic, low-tech tools like pen and paper.
2. "Drug dealers can use those too" is very different from "Drug dealers are commonly using those too, to deal drugs". Drug dealers surely use pen and paper sometimes. But how often are they using them? And are they using them to advertise and sell drugs, or just using them? (Note this also addresses your food analogy).
3. Facebook inherently collects massive amounts of evidence that pen, paper, and food don't.
> (reduction to the absurd) a disproof by showing that the consequences of the proposition are absurd; or a proof of a proposition by showing that its negation leads to a contradiction
Banning pens and paper isn't a consequence of forcing Facebook to not allow drug dealing.
Or in the contradiction sense, forcing Facebook to not allow drug dealing does not lead to an absurdity of everyone being forced to ban pens and paper.
1. We can enforce the law on Facebook in ways we can't with completely agnostic, low-tech tools like pen and paper.
2. "Drug dealers can use those too" is very different from "Drug dealers are commonly using those too, to deal drugs". Drug dealers surely use pen and paper sometimes. But how often are they using them? And are they using them to advertise and sell drugs, or just using them? (Note this also addresses your food analogy).
3. Facebook inherently collects massive amounts of evidence that pen, paper, and food don't.