Re: Not useful
It's called an error margin.
The equation is perfectly fine, so long as you account for your potential error.
And when you do that, we know the number of planets quite well. The number of intelligent beings is an estimate, of course, but it has limits. We know there can't be intelligent life on every planet. We know there can't be no intelligent life. So you get a nice range of measurements of where it's MOST LIKELY to lie and you apply those to the equation.
That gives you an answer of "what are the chances" with a nice error margin. And, fortunately, that error margin can be read as either a "most likely minimum chance" and "most likely maximum chance". The most likely minimum is basically zero. The most likely maximum is... well... tiny. So we can say, with some degree of accuracy, that the chances of finding any communicating civilisation at all are... tiny.
It's not hard. That's GCSE science. State your units. Calculate the possible error in your measurements.
And the Drake equation tells you that you won't observe life out there. And it only rarely gets revised up (e.g. the latest round of planet-detections in the last 20 years). And it more often than not gets revised further down (as here - even if they were around broadcasting for 10,000 years, we might never have detected them, and 10,000 years seems an oddly long time for a civilisation to be stuck on producing arbitrary and strong EM emissions).
At the end of the day, it's statistics, so it could all be "wrong". But it's not actually wrong. It's a probability, that you can calculate. We might find an intelligent civilisation next door (in solar terms), which is a billions-upon-billions-to-one chance. But it could happen and we still wouldn't be "wrong". It just may be fluke and the next one might never happen, statistically.
If you think statistics are wrong, you may as well never do any science at all, ever. If nothing else, they give you an indication of where it's best to focus your efforts. Sure, it may not work out. But, on average, over the age of a civilisation like ours, the statistics will win out and provide you with the best possible solution. Rather than waste billions looking for aliens and never developing space-flight, we can say "Hey, it's worth poking around, but let's spend the most money on real science that's more likely to result in something more practical."