Personally I'm not a fan of hate speech laws. I support the right of Heather Herbert to say vile things about Ann Widdicombe, for example, and I'm glad that that wasn't considered criminal in and of itself.
People say horrible things all the time. If every single one was criminal it would be impossible for the police to police it. Especially given everyone has different opinions on things and different beliefs. For example to a vicar it might be hateful to say that god doesn't exist (given the vicar's job is predicated on god existing) or to Muslim it might be hateful to draw Mohamed (given this is forbidden in the Hadith).... and so on.
However, incitement to violence is illegal. I've never seen Palestine Action calling for people to use claw hammers or a weapon of their choice, yet they are proscribed and Bash Back are not. I have no fixed views on Israel v Palestine, other than lots of innocent people are being hurt on both sides. But Bash Back have admitted damaging property (e.g. Wes Streeting's office, a conference building in Brighton and the EHRC office) and are somehow not proscribed.
That aside, and back to your point...
That image is encouraging violence for the easily persuaded.
Exactly this. And possibly the already angry. There's a lot of anger around these days in polarised politics etc. Images like that doing the rounds with the easily persuaded and/or already angry are the opposite of helpful. The contrast between that and the women's groups peacefully protesting to keep women's sports etc is quite something. But the subject matter is interchangeable for some people. The "omincause" and "right side of history" thinking seems to take over at times.