This debate appears to hinge on the perception that his Lordship was asked / ordered (the link changes it mind part-way through) to step down and he agreed - and that this was simply because he attended this event, and did nothing wrong, and their may be a sub-plot regarding his religion. That makes it a witch hunt, and is unjustified.
The link does say that his Lordship was 'probed by party officials' - which suggests that there may be more to this than first appears.
Jeremy Corbin is many things, but he is not stupid.
He can see the folly in simply sacking someone for being in the wrong place at the wrong time as well as I can.
The fact that Lord Mendelsohn agree to step down without complaint also adds to my argument that more may have gone on than has been revealed thus far.
If the noble Lord is innocent, why was he sacked, and if he was innocent, why has he not protested from the rooftops that his treatment is unfair?
It may be as it seems, that Corbyn is using a sledgehammer to crack a nut and to be seen to be 'doing the right thing' and it may be that his Lordship has agreed no to rock the proverbial vote.
But I think my point is valid - there may be more to this than we know - so far.