The whole point of Democracy is that there are losers as well as winners. It is not up to political parties to accommodate those who disagree with them by accommodating their policies. Parties and the candidates who stand on their behalf must be able to justify their own views and polices to the electorate, without them being diluted by the outside influence of those who may actually fundamentally disagree with what the party believes in. Those on the fringe are better off advocating their policies better instead of voting for candidates of the party they do not support.  Very occasionally an open primary may allow an independent to seriously run, but this will be so rare that it will not compensate for having their independent platforms at elections.