Let me be clear from the outset: the majority of work in analytic philosophy of religion (PoR) does not aim to proselytize, but is concerned with fairly technical topics, such as the possibility of creaturely free will in heaven, the compatibility of specific divine attributes, or the evidential problem of evil. But some portion of PoR is clearly aimed at convincing the reader that religious belief (usually, Christianity, given the demographics of academic philosophy) is reasonable. To this end, philosophers construct sophisticated arguments, for instance, to show that religious belief does not require evidence, that religious faith is also, or even primarily, a matter of practical rationality, that the evidence is overwhelmingly in favor of theism, etc. Plantinga and Swinburne are good examples. Such philosophy of religion can be plausibly regarded as a form of proselytism--I'm using a wider term than the usual "apologetics", as apologetics is the more narrow notion of systematically defending a particular religious position. But I'm not entirely happy with the term proselytism either, since I also think that some of this PoR is aimed at those people who have religious faith, but who are wavering, for instance, because others tell them their faith is not rational. So I'll settle for proselytism cum apologetics as a not entirely satisfactory term for this type of PoR. Is it acceptable for philosophers of religion to engage in proselytism/apologetics?
Since many PoR authors are theists (according to 2 surveys - PhilPapers and my own - between 70 and 75%) it is perhaps not surprising that personal religious beliefs play a role in PoR. A passion for mathematics, an interest in science, a love of art, can be great motivations to engage in the philosophy of mathematics, science or art, respectively. But philosophers who engage in apologetic/proselytizing PoR clearly go beyond that. They are not only driven by a personal passion, but by a will to effect real-life changes in the world. In particular, I think it is plausible that they want public opinion to be more favorably disposed towards the religious beliefs they are propagating. This is not unique to PoR. No-one is surprised that practical ethicists who think animal suffering should be avoided write papers and books on the ethics of our dealings with animals, and that they hope to improve the way we treat animals. Or that political philosophers who believe that say, liberalism, is the best political view, hope to nudge real-world politics in adopting their liberalist views.
Nevertheless, the situation for PoR seems to be different. In an earlier blogpost, Kenny Pearce admonishes PoR practitioners not to engage in apologetics/proselytism. He writes: "Philosophy of religion, as practiced by religious believers, is often confused with apologetics. (Perhaps it is even so confused, on occasion, by some of its practitioners.)" and "[apologetics] is not the aim of the philosopher (qua philosopher). The philosopher aims instead to discover arguments which are such that people holding certain views (which real people do, or at least are likely to, hold) will, upon considering the arguments, be rationally obligated to endorse the conclusion." He furthermore insists "the philosopher [unlike the apologist] is not concerned with what will actually convince people, but only about what people rationally ought to be convinced by." In an unpublished paper, Ryan Nichols and Paul Draper argue that PoR is in a dire state, because there is a conflict of interest. Ryan writes in a comment on an earlier blogpost of mine that surveys the results of a survey on natural theology "My reading of the situation is that philosophy of religion is unhealthy, and further that your data are best understood as demonstrating a statistically significant conflict of interest."
I am wondering, though, why it would not be permissible for PoRs to engage in some form of apologetics or proselytism. My sense is that these reservations stem from an overtly narrow notion of philosophy as a discipline that does not aim to affect real changes in the world. If it is permissible for political philosophers, practical ethicists, and even philosophers of science (think of writings against Intelligent Design by philosophers of science like Michael Ruse) to try to affect public opinion, why would it not be permissible for PoRs who honestly believe the ideas they are promulgating? Perhaps this is because there is something morally or epistemic suspect with proselytism an sich (in the strictly religious sense). However, as H.E. Baber has argued, there are good practical reasons for why a religious believer would engage in proselytism. Perhaps there are also good epistemic reasons: if one is convinced that a given position is correct, why would one not seek to convince others that it is correct?
Let me stress that I do think a division of cognitive labor is a healthy and desirable thing, and since we are (I hope) seeking truth as philosophers, it is desirable that not *all* PoR is of the proselytizing/apologetic. And moreover, I think given confirmation bias that it is desirable that PoR is practiced by people from various perspectives: atheists, agnostics, religious believers (not only or mainly Christians, preferably). Even if we do not seek to actively engage in proselytism/apologetics, our philosophical writings will be influenced by our prior views. To take a less laden example, a contextualist in epistemology will come up with plausible philosophical arguments for why contextualism is true, even if she is dispassionately engaged in seeking the truth. Similarly, even when we are not writing apologetics, our prior religious beliefs or lack thereof will influence our conclusions. But I do not think this overall aim of rationality and truth-seeking is incompatible with engaging in apologetics/proselytism. I do not think that authors who engage in this form of PoR are confused about the nature or aims of philosophy, but rather, that they employ philosophy to affect desired changes in the world. I think this is a legitimate use of philosophy (as in the examples of political philosophy and practical ethics).