Similar trains of thought:

I can’t fix global warming by myself so I’m going to do nothing.

Politicians don’t listen to my age group so I don’t vote.

I can’t donate to every charity so I won’t donate to any.

Everyone else ignores traffic laws so why should I care?

Those aren't similar. Those are social goods that require people to do them en masse to work, and defeatist attitudes. In this case, logging off isn't a social good and I'm saying it won't do much. There are ways to maintain privacy, just not this one.

Intelligent people can disagree on the meaning of similar is seems.

Yet not every disagreement is intelligent.

Indeed, but one more step (staying logged out), absolutely cannot hurt, and can help.