Then one wonders why many of these "validation seekers" are prepared to selectively abandon the principle of sufficient reason
Oh, good grief. Not wanting to jump on your particular hobby-horse backwards, as you prefer to do, does not meant they're 'abandoning' anything, let alone the 'principle' of sufficient reason.
And fail to see that methodological empiricism itself finds no empirical evidence for thinking that empiricism is the only way to truth and reality (philosophical empiricism). In other words ,selective validation and scientism.
Nobody thinks empiricism has any objective proof, that's why we talk about 'validation'. No-one is suggesting that empiricism is the only way to truth and reality, there are offerings from mathematics and logic as well - not accepting divine revelation or deeply-felt sentiment without some equivalent level of proof or validation is the absolute opposite of arbitrarily dismissing anything, it's about having consistent standards. You want something to over-rule empirical findings, all you need is a reliable methodology... still.
I'm all for methodological empiricism, as much as you but that isn't warrant to claim it is the only way to truth or reality.
And if anyone says it is, you can stand right behind me and talk about someone rushing on stage to be funny, or something. But until anyone does actually suggest that, how about sticking to the point?
O.