I think that mockery is undeserved, although I would certainly go along with mocking many of the people who have used the Drake Equation as if it provides any sort of hard number about extra terrestial civilizations. As noted, we have little to no information about the actual values of most of the terms in the equation so any number that comes out is a handwaved tangle of guesswork and assumptions.
However, this misses the actual utility of the equation, which is much more “meta”1. The equation is good science in two different but related aspects.
The first is as a strawman basis for argument about extra terrestial civilizations. Certainly in most of the technical discussions I’ve had in my career, it was far easier to make progress by throwing out something, anything, that was at least plausible as a basis for dicussion and refinement. That’s what the Drake Equation is, the first step on a long journey to knowledge.
Secondly, having an equation to describe something is useful even if you don’t know any of the values it requires. It’s the same thing as graphing an equation. It doesn’t tell you what the literal answer is, but it can illustrate which values are important and how they relate to one another. It also reminds me of why electronic spreadsheets were such a driving force in the early computer industry. A spread sheet wouldn’t tell you what actual numbers represented your business, but playing with the spread sheet could tell you which values were most important and how sensitive the final value was to changes in the inputs. And as with the Drake Equation, it was a non-trivial risk that people could lose that subtle level distinction and start confusing the hypothetical with the real.
1 Ah, you were waiting for me to get on that hobby horse, weren’t you?