"There are many reasons people choose to convert. Some do so for love and marriage, others because they are looking for spiritual meaning. However, there are also those who convert to Islam as an alternative to the current liberal ideology. Especially after the terrorist attacks on the Twin Towers, converts tend to lean more towards political choices rather than spiritualism and personal choice.There's plenty of links in the original text.
In his book "Al Qaeda in Europe", Lorenzo Vidino expresses a similar viewpoint. Converts reach radical Islam through disillusionment with Western and European society. Especially with Islam, people convert as a form of social protest, with Islam serving as an alternative to neo-Nazi or anarchist groups.
This radicalization is not theoretical. Converts make up at the most 1-2% of the Muslim populations of different countries in Europe, but according to a recent study, they make up 5-6% of terrorists. According to Edwin Bakker, head of the Netherlands Institute of International Relations, converts tend to radicalism because they try to be as true to their religion as possible. In other words, for those converts, Islam is seen as a non-democratic movement, set on destroying liberalism.
Esther, International Relations, 01.15.08