The statement "Secularism was an outcome of 20th century humanistic radicalism" suggests a specific historical and philosophical lineage for secularism, linking it to a particular intellectual and social movement. While this perspective captures an important aspect of secularism's development, it is crucial to analyze its nuances and acknowledge other contributing factors.

Humanistic Radicalism and Secularism: Humanistic radicalism, broadly understood, refers to intellectual and social movements that prioritize human reason, ethics, and well-being over divine authority or traditional dogma. It often advocates for fundamental changes in societal structures to achieve greater human freedom, equality, and progress. In the 20th century, this radical humanism manifested in various forms, including:

1. Rejection of Religious Dogma: Humanistic radicalism often challenged the absolute authority of religious institutions and doctrines, advocating for a worldview based on scientific inquiry, critical thinking, and empirical evidence. This directly contributed to the idea that public life and governance should not be dictated by religious tenets.

2. Emphasis on Individual Autonomy and Rights: A core tenet of humanism is the dignity and autonomy of the individual. Radical humanists championed individual liberties, freedom of conscience, and the right to self-determination, which are foundational to secular principles like freedom of religion (and freedom from religion) and non-discrimination based on belief.

3. Social Justice and Equality: Many humanistic radical movements were deeply concerned with social justice, equality, and the alleviation of human suffering. They often saw religious institutions as perpetuating inequalities or hindering social progress. Secularism, by advocating for a state that treats all citizens equally regardless of their religious affiliation, aligns with this pursuit of justice.

4. Enlightenment Legacy: While 20th-century humanistic radicalism built upon earlier Enlightenment ideals, it often pushed these ideas further, advocating for a more complete separation of church and state and a more thoroughgoing rationalization of public life. The horrors of religious wars and the perceived irrationality of religious fundamentalism in the modern era further fueled this radical push for secular governance.

Nuances and Other Factors: While humanistic radicalism played a significant role, it's important to consider other factors and historical trajectories:

1. Historical Precedents: Secular ideas have roots much earlier than the 20th century, tracing back to the Enlightenment in Europe (17th-18th centuries) with thinkers like Locke, Voltaire, and Rousseau, who advocated for religious tolerance and the separation of church and state. The American and French Revolutions were pivotal in institutionalizing some of these principles.

2. Political Pragmatism: Secularism also emerged from political necessity, particularly in diverse societies or those recovering from religious conflicts. A neutral state, not favoring any particular religion, was seen as a way to maintain peace, ensure stability, and govern a pluralistic population effectively. This pragmatic aspect is distinct from purely ideological humanism.

3. Rise of Nation-States: The consolidation of modern nation-states often required a unified civic identity that transcended religious loyalties. Secularism provided a framework for national unity by placing citizenship and shared civic values above sectarian affiliations.

4. Scientific and Industrial Revolutions: The advancements in science and technology, coupled with industrialization, led to a decline in the perceived authority of religious explanations for the natural world and social phenomena. This shift towards a more rational and empirical worldview created fertile ground for secular thought.

In conclusion, the statement holds considerable truth. 20th-century humanistic radicalism, with its emphasis on human reason, individual rights, social justice, and a critical stance towards traditional religious authority, indeed provided a powerful impetus for the development and institutionalization of secularism. However, secularism is also a product of a longer historical evolution, political pragmatism, and broader socio-economic transformations, making it a multifaceted phenomenon rather than solely an outcome of one specific intellectual current.