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It was scientific enough to draw federal funds into the SETI project. It's based upon counting billions of stars and trying to figure out which ones are the most likely to harbor intelligent life. The sample base is in the trillions.

Here's a sampling of the controversy:

The chances of getting accidentally synthesized left amino acids for one small protein molecule is one chance in 10^210. That is a number with 210 zeros after it! Such probabilities are indeed impossibilities. The number is so vast as to be totally out of the question.

http://www.infidels.org/library/modern/richard_carrier/addendaB.html

Hubert Yockey's article "Self Organization Origin of Life Scenarios and Information Theory" in Journal of Theoretical Biology 91 (1981) pp. 13-31 (this is an extension of work done by him in 1977 in vol. 67 of the same journal). The objective of his paper is not to prove special creation (he actually rejects such theories as useless), but to argue that alien life is so improbable that we ought to shift science to draw talent and funding away from projects like SETI and into "research on the origin of life." In his own abstract, he presents his conclusion as "belief in little green men in outer space is purely religious not scientific." But his assumptions are as faulty as those made by creationists, although his approach is much more sophisticated--and above all, he does not generate any actual estimates of probability. He tries to argue that only 10^5 arrangements of a protein 100 amino acids long, out of a total possible 1.26 x 10^130 arrangements, are of concern to biology, if we assume a 4-bit code. Though he does not state this explicitly, this means the odds against life starting, if it had to start with just such a protein, would be 1 in 10^125.

The Drake occasion is pseudoscience masquerading as science. Each of the numbers is nothing more than a prejudiced guess. N=N*fp ne fl fi fc fL where N is the number of stars in the Milky Way galaxy; fp is the fraction of stars with planets; ne is the number of planets per star capable of supporting life; fl is the fraction of planets where life evolves; fi is the fraction where intelligent life evolves; and fL is the fraction of planet's life during which the communication civilizations live. The problem is that none of the terns can be known, and most cannot even be estimated. The only way to work the equation is to fill in with guesses. And guesses are merely expression fo prejudice. There can't even be "informed guesses" If you need to state how many planets with life choose to communicate, there is simply no way to make an informed guess. It is simply your prejudiced belief for or against the possibility that shows through. Therefore, depending on your "guesses", the equation gives you a value of anything ranging from billions and billions to zero. An equation that can have any value has no value.
I guess there's a reason why Sagan's "equation" to "prove" nuclear winter took the form of: Ds= Wn Ws Wh Tf Tb Pt Pr Pe.....etc. (The amount of tropospheric dust = #warheads x size warheads x warhead detonation height x flammability of targets x target burn duration x particles entering the troposphere x particle reflectivity x particle endurance.....etc.) The original study here mapped out different wartime scenarios and assigned numbers to some of the variables, but even so, the remaining variables were and are simply unknowable. Nobody knows how much smoke will be generated when cities burn, creating particles of what kind, and for how long. No one knows the effect of local weather conditions on the amount of particles that would be injected into the troposphere or how long they would remain there, and so on.
This is nothing more than consensus....and consensus isn't science. The work of science has nothing whatever to do with consensus. Consensus is the business of politics. Science, on the contrary, requires only one investigator who happens to be right, which means that he or she has results that are verifiable by reference to the real world. In science, consensus is irrelevant. What is relevant is reproducible results. The greatest scientists in history are great precisely because they broke with consensus.
This article merely states the prejudice of the scientists. They believe in the existence of extraterrestrial life. This, in itself, is neither good nor bad. In fact, it may open them to looking at things in ways other people don't, since, following consensus, most scientists dismiss the simple possibility of life existing elsewhere or, if it does exist, of it being able to make its existence known to us. But don't make the mistake of taking their belief and treating it as evidence, which is a mistake scientists and the general public do with increasing frequency!