> "The next time I talk to an unreasonable Christian ... I will just say [stuff]"

A lot of the "unreasonableness" in modern American Christianity has a specific basis; understanding that basis is important if you want to respond effectively. Christian Liberalism was an intellectual movement in the late 1800s that sought to discard the supernatural aspects of scripture by inappropriately assuming most of it was figurative; Fundamentalism arose in the early 1900s as a response that included a series of overreactions -- treating scripture hyper-literally, embracing anti-intellectualism, and treating even the smallest everyday occurrences as supernaturally significant. While few today claim the label, a lot of ordinary American Christians have been influenced to some degree by this sort of thinking.

Correcting this sort of unreasonableness is not as simple as telling them they're wrong and stupid; a less snarky and less belittling approach is usually more effective. Declaring (inaccurately) that they're "not true Christians" doesn't help, but rather, it is helpful to explain the details of why they are mistaken and help them understand better. (The downside is that this takes more effort than the standard reddit-style "OMG UR DUMB" comment; the upside is that it's actually productive.)

> "their experience ... can be misconstrued as blind chance, can't be reproduced, and/or can't be falsified"

It is tremendously important to treat one's experiences just like any other sort of data. One of the mistakes certain people make is treating common events as significant. One mistake a different group makes is treating all experience as insignificant. Do not be a part of either of those groups.

Recall that "falsifiability" is a statement about theory, not about data. An experience is not falsifiable. A generalization drawn from experience should be (otherwise it is a worthless generalization.)

Also recall that a lot of types of data cannot be reproduced -- historical observations, astronomical observations, fields like economics, and so on. We have systems and best practices for dealing with non-repeatable data; if it's carefully recorded, it can be analyzed and discussed rationally. It's not as good as lab experiments, but it's what you have to settle for when dealing with systems that can't be constrained to the lab.

The key to dealing with experience as data is to understand the probabilities involved. Finding one's car keys after prayer and searching is not particularly signficant (after all, one normally finds their car keys after searching); praying and hearing turn-by-turn directions in your head to a place you've never been is significant. While both scenarios could theoretically be "blind chance", one is significantly harder to justify in that manner.

> "Christianity as a whole can ... eventually coalesce ...?"

The Bible isn't written like a legal document or a mathematical proof. In attempting to understand a fairly complex and sophisticated system with many parts contributing to the whole, there are estimates and prioritizations and judgment calls involved. Thus, there is a certain expected level of disagreement that is reasonable -- and modern Christian theologians are at that point (the "rank and file" are a little behind.) Most of the seemingly huge disagreements between churches or denominations are actually small disagreements about how to balance multiple important factors (I say this as a pacifist married to a defense contractor -- we are not "totally opposite", we just disagree on the relative importance of two statements.)