I appreacite your concern, but is there something substantial to fear?
I have not crossed the line into credible death threats; this is first amendment protected speech. If I get a visit from the secret service I will consider it a win for having wasted their time.
And if Trump starts rounding up "online leftists agitators" or "antifa" or whatever to put in his concentration camps, I'll probably already be in the camps for a different reason.
I think an ethical shooter would take every reasonable precaution to avoid hitting the human shield.
But in the vanishingly small hypothetical where it could not be avoided, then I would still consider the shooter a hero, yes.