From the outset, it became quite clear that those who control the newspapers - who, probably through self-interest, were in favour of the Conservative austerity programme - wanted Corbyn out and would do anything to discredit him. On top of that, Corbyn is persona no grata to those in power in Israel and people who were fully supportive of Israeli policies towards the Palestinians.
Corbyn was a threat to the status quo in regard to this country's economic and social policies and in regard to this country's stance regarding Israel. There does not appear to be much in his life that can be used to "dish the dirt" so something needed to be found to discredit him and anyone who supported him.
Racism can be quite a difficult allegation to support or refute so it has been quite a useful one to throw at Corbyn and people who are broadly in favour of many of his views. But if there is clear evidence that a group of people or an individual has been racially abused or subject to threatening behaviour my understanding is that that would be a criminal offence and individuals who are alleged to have committed these offences should be dealt with through the legal system.
There are dozens of examples of Conservative and UKIP officials and members making racist remarks - eg the Conservative councillor who captioned the photograph of a woman in a burka standing next to some black bin bags "'I saw her standing there and I told her she had three beautiful children." Or Boris Johnson referring to black children as "piccaninnies". There are too many of these sorts of examples to count.
I think black and Asian people who have since the 50's been the target of racist comments and who have been discriminated against in all areas of public life - education, employment, housing, the justice system, etc, etc must be perplexed as to why their hopes and ambitions continue to be adversely affected by unconscious or deliberate racism and yet their issues are rarely addressed. Instead, simply expressing a view about another country's behaviour means that a person will be labelled as "racist".