It's only appears tenuous because the subjective choices you have to make when using frequentist methods are made for you by the developer of the method.
It's less comfortable to use Bayesian methods because you have to be explicit about your assumptions as the user, which opens your assumptions up for easier inspection. There's also way less specific information implied by priors than most people think. Informative priors should try to make distinctions between something that's reasonable-ish and something that's essentially infinity (take pharmacokinetics for example, the diffusion velocity of a molecule in your blood stream shouldn't have a velocity near the speed of light in a vacuum should it?). They should not be forcing your model to achieve a particular result. Luckily, because of the need to explicitly state them in a Bayesian analysis, it's much easier to determine if they were properly set.
Prior specification is essentially problem domain-informed regularization where you can actually hope to understand if the hyperparameter is going to work or not.
It's less comfortable to use Bayesian methods because you have to be explicit about your assumptions as the user, which opens your assumptions up for easier inspection. There's also way less specific information implied by priors than most people think. Informative priors should try to make distinctions between something that's reasonable-ish and something that's essentially infinity (take pharmacokinetics for example, the diffusion velocity of a molecule in your blood stream shouldn't have a velocity near the speed of light in a vacuum should it?). They should not be forcing your model to achieve a particular result. Luckily, because of the need to explicitly state them in a Bayesian analysis, it's much easier to determine if they were properly set.
Prior specification is essentially problem domain-informed regularization where you can actually hope to understand if the hyperparameter is going to work or not.