Perhaps their fear was based on what they considered the allure of Gentile woman. They certainly spend a lot of time discussing women in the Talmud and not necessarily in a positive manner. Many of the rabbis in the Talmud were concerned with the power of the sexual attractions of men and women. As they commented, "No one is immune to the ravages of an illicit attraction." And in reference to why woman have this undesirable effect on men they stated, "There is only one real cause of jealousy among women—sex appeal." http://hubpages.com/hub/Why-Karaism-The-Essential-Talmud

You may have noticed that the list of prohibited marriages never included women not of Jewish birth. In fact, there is a total absence of any such prohibition from all of Leviticus. Therefore one must conclude that it was not prohibited. It must be remembered that Karaism is a patriarchal society with inheritance of one’s birthright passed down father to son but as you can read in my hub http://hubpages.com/hub/The-Ethiopian-Princess there was a purge of non-Jewish wives from the community as soon as the exiles from Persia returned to Israel.

Over the years I have been accused countless times of belonging to what mainstream Judaism considers a heretic sect. From being called “Aher” or 'the other', to having my knuckles rapped with a yardstick by the Rabbis that taught me for having dissenting opinions and contrary beliefs. It’s not easy to accept being outside the mainstream and being punished for being so. But that has been the history of the relationship between Karaites and Rabbanites for over a millennia now. The former punished by the latter for holding heretical beliefs.