It's a defense mechanism. If people are having their liberties stripped away and are being subject to violence over something so little as a harmless meme, then it could happen to anybody including yourself.
But if there are details not being reported on that would give the border agents a legitimate reason to assault the victim here, like real threats against government officials, being a menace through customs, or otherwise something any normal person would not do, then the victim deserved it and normal law-abiding people can continue to feel secure knowing they're safe from this treatment so long as they don't do whatever the victim did to deserve that treatment.
There's a similar effect for sexual assault victims: "They were asking for it because of what they were wearing/who they misplaced their trust in/where they chose to walk alone at night". It's all designed to put fault on the victim in order to maintain a false sense of security for the average person.