A "holy war" between Bayesians and frequentists exists in the modern academic literature for statistics, machine learning, econometrics, and philosophy (this is a non-exhaustive list).

Bradley Efron, who is arguably the most accomplished statistician alive, wrote the following in a commentary for Science in 2013 [1]:

The term "controversial theorem" sounds like an oxymoron, but Bayes' theorem has played this part for two-and-a-half centuries. Twice it has soared to scientific celebrity, twice it has crashed, and it is currently enjoying another boom. The theorem itself is a landmark of logical reasoning and the first serious triumph of statistical inference, yet is still treated with suspicion by most statisticians. There are reasons to believe in the staying power of its current popularity, but also some signs of trouble ahead.

[...]

Bayes' 1763 paper was an impeccable exercise in probability theory. The trouble and the subsequent busts came from overenthusiastic application of the theorem in the absence of genuine prior information, with Pierre-Simon Laplace as a prime violator. Suppose that in the twins example we lacked the prior knowledge that one-third of twins are identical. Laplace would have assumed a uniform distribution between zero and one for the unknown prior probability of identical twins, yielding 2/3 rather than 1/2 as the answer to the physicists' question. In modern parlance, Laplace would be trying to assign an "uninformative prior" or "objective prior", one having only neutral effects on the output of Bayes' rule. Whether or not this can be done legitimately has fueled the 250-year controversy.

Frequentism, the dominant statistical paradigm over the past hundred years, rejects the use of uninformative priors, and in fact does away with prior distributions entirely. In place of past experience, frequentism considers future behavior. An optimal estimator is one that performs best in hypothetical repetitions of the current experiment. The resulting gain in scientific objectivity has carried the day, though at a price in the coherent integration of evidence from different sources, as in the FiveThirtyEight example.

The Bayesian-frequentist argument, unlike most philosophical disputes, has immediate practical consequences.

In another paper published in 2013, Efron wrote [2]:

The two-party system [Bayesian and frequentist] can be upsetting to statistical consumers, but it has been a good thing for statistical researchers — doubling employment, and spurring innovation within and between the parties. These days there is less distance between Bayesians and frequentists, especially with the rise of objective Bayesianism, and we may even be heading toward a coalition government.

The two philosophies, Bayesian and frequentist, are more orthogonal than antithetical. And of course, practicing statisticians are free to use whichever methods seem better for the problem at hand — which is just what I do.

Thirty years ago, Efron was more critical of Bayesian statistics [3]:

A summary of the major reasons why Fisherian and NPW [Neyman–Pearson–Wald] ideas have shouldered Bayesian theory aside in statistical practice is as follows:

1. Ease of use: Fisher’s theory in particular is well set up to yield answers on an easy and almost automatic basis.
2. Model building: Both Fisherian and NPW theory pay more attention to the preinferential aspects of statistics.
3. Division of labor: The NPW school in particular allows interesting parts of a complicated problem to be broken off and solved separately. These partial solutions often make use of aspects of the situation, for example, the sampling plan, which do not seem to help the Bayesian.
4. Objectivity: The high ground of scientific objectivity has been seized by the frequentists.

None of these points is insurmountable, and in fact, there have been some Bayesian efforts on all four. In my opinion a lot more such effort will be needed to fulfill Lindley’s prediction of a Bayesian 21st century.

The following bit of friendly banter in 1965 between M. S. Bartlett and John W. Pratt shows that the holy war was ongoing 50 years ago [4]:

Bartlett: I am not being altogether facetious in suggesting that, while non-Bayesians should make it clear in their writings whether they are non-Bayesian Orthodox or non-Bayesian Fisherian, Bayesians should also take care to distinguish their various denominations of Bayesian Epistemologists, Bayesian Orthodox and Bayesian Savages. (In fairness to Dr Good, I could alternatively have referred to Bayesian Goods; but, oddly enough, this did not sound so good.)

Pratt: Professor Bartlett is correct in classifying me a Bayesian Savage, though I might take exception to his word order. On the whole, I would rather be called a Savage Bayesian than a Bayesian Savage. Of course I can quite see that Professor Bartlett might not want to admit the possibility of a Good Bayesian.

For further reading I recommend [5], [6], [7].

[1]: Efron, Bradley. 2013. “Bayes’ Theorem in the 21st Century.” Science 340 (6137) (June 7): 1177–1178. doi:10.1126/science.1236536.

[2]: Efron, Bradley. 2013. “A 250-Year Argument: Belief, Behavior, and the Bootstrap.” Bulletin of the American Mathematical Society 50 (1) (April 25): 129–146. doi:10.1090/S0273-0979-2012-01374-5.

[3]: Efron, B. 1986. “Why Isn’t Everyone a Bayesian?” American Statistician 40 (1) (February): 1–11. doi:10.1080/00031305.1986.10475342.

[4]: Pratt, John W. 1965. “Bayesian Interpretation of Standard Inference Statements.” Journal of the Royal Statistical Society: Series B (Methodological) 27 (2): 169–203. http://www.jstor.org/stable/2984190.

[5]: Senn, Stephen. 2011. “You May Believe You Are a Bayesian but You Are Probably Wrong.” Rationality, Markets and Morals 2: 48–66. http://www.rmm-journal.com/htdocs/volume2.html.

[6]: Gelman, Andrew. 2011. “Induction and Deduction in Bayesian Data Analysis.” Rationality, Markets and Morals 2: 67–78. http://www.rmm-journal.com/htdocs/volume2.html.

[7]: Gelman, Andrew, and Christian P. Robert. 2012. “‘Not Only Defended but Also Applied’: The Perceived Absurdity of Bayesian Inference”. Statistics; Theory. arXiv (June 28).

Dude, I'm being genuinely curious about what "holy wars" he's talking about.

For lots of "holy war" anecdotes, see The Theory That Would Not Die by Sharon Bertsch McGrayne.

...I can't even tell if he's talking about some stupid overblown bullshit, or if he's just exaggerating what is actually a pretty low-key difference in opinion.

Do you consider personal insults, accusations of fraud, or splitting academic departments along party lines to be "a pretty low-key difference in opinion"? If so, then it is "overblown bullshit," otherwise it isn't.

Ilya responded to your second paragraph not the first one. metric vs. imperial or flash vs. html5 are not good analogies.