Many people who are not members of the Green Party, and who would not at this time vote for it either, nonetheless feel sympathetic towards it and regard it as a valuable element on the political scene (I am myself such a person). They think its concerns are important ones, and they wish it well, in a general way. So it is an important matter if this Party, which aims to become part of the mainstream of political life in the UK, is unwilling to do what's needed to ensure that its commitment to anti-racism is a genuine one. If, instead, it turns into an institution that only rejects racism directed at the groups which it politically favours, and regards with complaisance discrimination and racist discourse targeting other groups, then that general well-wishing will (and should) evaporate.
I can add nothing whatever to what Eve Garrard says so eloquently over on normblog.