I’m not quite sure what the EBU can do about any ‘extremists’ (as you call them) attending the event who may boo, jeer or take a physical approach and simply turn their back, for example. Again, it will be interesting to see how this is handled!
I am not talking about booing/jeering but rather about incitement of hatred/physical violence. The former, I would believe the Israeli delegation would have expected such reactions and that would be the least of their concerns. As for the latter, EBU and the Swedish government would then have to do their utmost to ensure this is being taken care of, regardless Israel partakes in the competition or not.
And also, we are also on the assumption that most of the people attending the contest live would boo/jeer at Israel/Eden.
For all we know, it could just be a small (vocal) fraction and could be dealt with swiftly.
We would know once the dress rehearsals start, it will give an indication.
I am sure the Israeli delegation would have employed extra private security on their own, which I believe they always have.
Anyway, it's too early to say. We will know on the 10th March if Israel will be part of the contest.
Any discussion now about security seems pretty moot.