“I don’t know the context, but that sounds more like an argument used to justify the project to incurious people than his own reason for doing it.”

That may be why Drake said such a thing, but that doesn’t justify resorting to it tactically. I’d consider doing so to be disingenuous, and careless. It’s like what Feynman said when some physicist fretted about how to convince the public into supporting funding for expensive accelerator labs. The gentleman in question wanted to assure the public that there must be practical spinoffs from such endeavors which will benefit the less basically curious among the taxpayers. Feynman’s take was that if there are no such spinoffs, then it’s dishonest to insist that there are. The public have some entitlement to know the real relationship between their dollars and where those dollars go, to allow them to make well-informed decisions as to what they think amounts to acceptable investments.

And so, assuming that SETI can make no promises as to return on investment, it would be effectively a lie to say otherwise just to gather funding. Telling people what they want to hear instead of the truth is called “gaining their confidence”, and is used by criminal-types routinely to sell anything from siding to used cars to pocket fishermen. It’s not scientifically honest.

There are only certain circumstances in which I’d agree with scamming people. Finding one’s self trapped in a Nazi concentration camp is one such circumstance. Soliciting money from those whom you ostensibly respect is not.