Without thinking about the etymology, many of us use Latin words every day: criteria/criterion, museum, auditorium, agenda, data, premium, for example.
For the most part, we take those words and subject them to our English rules. Except for criterion and data, we simply add an S to make the plural and no longer realize that the Latin plurals are musea, auditoria and premia. The singular of agenda is agendum, but we never see that any more.
One word losing the distinction between singular and plural is data. That is the plural form (datum is the singular), but we rarely see or hear the latter. It is becoming standard English to use “The data is confusing.” In fact, I’m guessing most people would be surprised to hear “The data are confusing.” Because data is not something easily separated into its components, this swing toward the ubiquitous singular is understandable.
The distinction between criterion (singular, referring to one component) and criteria (plural, meaning more than one component) still exists, and I admit I cringe when I hear or see a sentence such as, “I have only one criteria for cooking Thanksgiving dinner: someone else has to do it.” Keep using the singular and plural forms of these words; they still carry meaning.