Let's say a person justifies adopting a set of factual beliefs on the grounds of wanting to participate in an ideological based social group. Or on the grounds of self-committing to some ethical norms that are asserted to be related to that particular set of factual beliefs. Or on the grounds that holding this set of factual beliefs is psychologically comforting because it provides purpose and meaning. Or on the grounds that these factual beliefs are matters of personal preference or of faith and are thus self-justifying. Professing this set of factual beliefs has thus become entangled with ongoing social and ethical commitments and activities and motivations. Accordingly, this person claims a self-dependency on holding this set of factual beliefs.
Given this context, is it now unethical for those us who disagree with that set of factual beliefs to publicly argue against them given that there is some risk that such a person could, partially or wholly as a result of exposure to those arguments, lose their beliefs? Clearly, there is reason here to be cautious. We do not want to harm anyone by isolating them socially, or by telling them they should give up on ethical commitments, or by telling them there is no meaning to their life or purpose for them to pursue. As secular humanists we are people focused, we oppose abandoning people. We abandon transcendence, not ethics, nor meaning, nor purpose.
Some humanists argue that we should distinguish between people who respect everyone's civil rights and those who do not. They say it is ethical to argue against the beliefs of those people who fall in the latter category only. But is this distinction practical to implement? Not if one of the goals is to challenge bad justifications for factual beliefs. The same faulty reasoning is common to both sets of people.
Why focus on challenging bad justifications for factual beliefs? Because, like it or not, it is not enough to have good ethical commitments. Ethical commitments are important, but so is proper justification of factual beliefs. Arguably, the worst atrocities have historically been committed by ethical people with the best intentions. What goes wrong? Part of the answer is that these people tended to be undisciplined in how they justified their factual beliefs. Religion in general is built upon, it depends on, and it encourages, promiscuous adoption of factual beliefs. This is a problem with potential real world negative consequences, and it is not a problem confined to "bad" religion as opposed to "good" religion.
People who make themselves dependent, socially, psychologically, or otherwise, on a particular set of factual beliefs have thereby made a mistake. This is a problem in and of itself as it interferes with good reasoning. Furthermore, this is an unnecessary problem. This problem is a result of people turning themselves into ideologues and prioritizing ideology over reasoning. Rather than perpetuating this problem by falsely declaring it ethically taboo to challenge dubious factual beliefs that are held without proper warrant, it is better in the long run to deal with adults as adults. It is an elitist attitude to say that as non-religious non-believers we should unilaterally censure our speech to protect religious believers from themselves. They can stand up for themselves also. People who experienced a difficult transition from religious belief to non-belief often say that they are now glad that they made that transition. By speaking out publicly for non-belief, maybe we can contribute to making this transition less difficult for religious individuals.