It's horrible to see this happening.
Not sure why you'd compare fighting for continued EU membership to opposing the Iraq war or fighting for civil rights. Leaving the EU is bad, but it's far from equivalent to Jim Crow or what the US and UK did to the Arab/Muslim world. And especially not
when(unlike the campaigns against Jim Crow in the US, apartheid in South Africa, and the unwinnable wars in Vietnam, Central America and Iraq/Afghanistan) the only possible outcome is a large gain in seats for UKIP?
And is there any way to create the conditions for any sort of progressive electoral victory by doing so?
All Corbyn was guilty of was admitting, during the referendum campaign, that people had legitimate grievances about the EU, especially about the economic consequences EU membership has had on the North and Northeast. If EU membership had created prosperity in those regions, Leave would never have had a chance.
But creating prosperity in the North and the Northeast would require state intervention in the economy, because the "free market" will always be trying to grind that part of the UK into the dirt for the crimes heavy trade union membership and die-hard opposition to Thatcherism.
What I think Corbyn is trying to do here is to save the best of the EU tie(ease of travel and the anti-discrimination policies) yet create the space for a future UK government to bring in anti-austerity economic policies. That is, he's trying to do what you want but simply using different tactics and trying to get Labour out of the constraints imposed by staying strictly in the Leave/Remain duality
Can you suggest any way to fight austerity and for workers' rights AND fight for continued membership in an institution that will never allow anyone any space for doing so? That would be the best possible way, but how could it be possible?