No sure, I get the point. My grandfather was an orthodox Jew, although that clearly didn't last after marrying a Christian, he remained Jewish. His grandfather emigrated here from Poland at the turn of the century, and of course the relatives who stayed behind were murdered in the War.
Not that you need a Jewish background to have an opinion, but just to demonstrate I'm not being flippant, even if the earlier post did. I have total sympathy for the Iranian Jewish poster and the anti-Semitism she has faced.
I'd explore the point you rightly make about having Jewish people on a march doesn't make it anti-Semitic, and say that having some people with Hamas symbols also doesn't mean a whole march is anti-Semitic. I am surprised that people on MN can claim to know the reason why any particular person, Jewish or not, goes on a march.
It is perfectly acceptable to believe that what the IDF and Israeli government is doing in Gaza (and the West Bank) is criminal, and disproportionate, and support a two-state solution, and not be anti-Semitic in any way. Indeed, as a supporter of Israel, watching the horrors on the news I can't help but think not only is it totally immoral what Israel is doing to the people of Gaza, but long term it's going to perpetuate violence ad infinitum when orphaned children grow up and take revenge for seeing their whole families buried alive under rubble of their homes.....
My grandfather used to send money to support Israel in the early days post WW2, but he stopped after the Six Day War as he became uncomfortable with what the country was doing.
Part of the problem is education- in primary children learn about WW2, but it's just Britain alone/evacuation/Battle of Britain/D-DAy nothing else. I've tried to include a few lessons on the Holocaust and Hitler's rise to power, including using some excellent resources from the Holocaust Education Trust and Y6 children have really found this engrossing and fascinating, but with the obsession in my school and presumably others about sticking to the plan, this isn't always easy. I can't speak for secondary but I wonder- I have talked to pro-Palestinian protesters about anti-Semitism and I struggled to find any nuance. It's either one or the other.
Anyway, this seems a bit rambling, but I don't believe every person waving a Palestinian flag on a march is anti-Semitic. Calling for a two-state solution isn't anti-Semitic, nor is calling for the end of the Gaza occupation. I think if the latter two things were to happen, this would increase the chances of peace in the Middle East, and be of benefit to Israel.