Drake equation shows a high probability of alien life

Question: Do aliens exist?
Position‹3 of 4›: Probably, but we don’t yet have proof of alien life
Argument‹2 of 2: Drake equation shows a high probability of alien life

The argument

The Drake equation attempts to compute the probability of alien life civilisation based on a number of factors. According to Frank Drake, the equation gives a probability. According to this equation is extremely unlikely that Earth is only place in Galaxy where civilization has been developed. Further data on exoplanets allowed to refine some of Drake's equation parameters,

Premises

[P1]The Drake equation estimates the probability of alien civilisations from a number of astronomical factors. [P2] Its result makes it extremely unlikely that Earth is the only place in the galaxy where civilisation has developed. [P3] New exoplanet data has refined and supported its parameters. [C] Therefore, the Drake equation shows a high probability of alien life, so aliens probably exist even without proof yet.

Counter-arguments

Some of the parameter values of Drake equation are simply guesses, or can have a very high variance. Therefore the range of values of its solution are so large that can not be of practical usage

Rejecting the premises

[Rejecting P1] The equation does not compute a probability. It is a way of decomposing a question into factors so they can be discussed separately — Drake presented it as an agenda for research rather than a calculation — and it produces a number only once every factor is supplied. [Rejecting P2] The counter-argument on record identifies the fatal difficulty: several terms are unconstrained by any evidence. The fraction of habitable worlds on which life arises, the fraction of those on which intelligence appears, the fraction that develop detectable communication, and above all the average lifetime of such a civilisation are estimated from a single instance, so the output can be varied across many orders of magnitude by choosing plausible-looking inputs. A result that can be made to say anything says nothing. [Rejecting P3] Exoplanet data has constrained only the astronomical terms — how many stars have planets, and how many of those lie in habitable zones. Those were always the least contentious factors, and tightening them does not narrow the range the biological and sociological terms produce. [Rejecting C] The argument also ignores the observation that motivates the opposing view: no signal, artefact or trace has been detected despite decades of searching, which is exactly what the equation's optimistic readings would not predict. (The body is a typo-affected stub and is a candidate for replacement.)