Up to about the 1960�s it was quite acceptable and legal to discriminate on the grounds of race. (Remember the accommodation adverts, �No Blacks, No Irish, No Dogs?).
Gradually it became unacceptable and latterly illegal. Legislation was passed by Parliament because that is what most people (or more precisely most MPs) wanted.
There is no reason why this situation should be permanent. If enough people can persuade enough MPs to reverse that legislation then that is what should be done. If a party stands on such policies (and by implication probably would not be the party to best represent everybody) then that�s democracy for you.
My MP (who happens to be a Tory) does not best represent me. He does not vote the way I would like him to on key issues such as immigration. The Tory party will not carry out my wishes on immigration if and when it is elected to government. But I do not wish the Tories (or indeed any other party) to be banned from standing just because of that.
For some people democracy is fine provided it delivers just what they want and what they think everybody else should have.
Politics is just not that straightforward and now that the worm is turning slightly it is no use moaning and wanting to change the rules.