Why would a political party avoid associating with an interest group that holds radical principles? to prevent groups that have
more popular views from running successful campaigns to encourage various interest groups to create their own political parties and run campaigns so they can hide purposes and ideologies from voters so they don't have to be enforced once in office so they can gain the support of as many voters as possible and get their members into office
If you avoid associating with a group with radical principles, you risk losing voters from any group that is not radical and from any radical group that is not the one that you have supported. By supporting a radical group, you diminish the amount of people who relate to you in a very significant way. The answer is:
so they can gain the support of as many voters as possible and get their members into office
