The late Carl Sagan was often looked upon by pro-ETH ufologists as a debunker.
While that may have been true later in his life, at least by the sometimes narrow standards of pro-ETH ufologists (they of the "pelicanist" and "Klasskurtzian" labels), it certainly wasn't the case earlier in his career. Here's a letter to Sagan from a REAL debunker, Dr. Donald Menzel, that gives an idea of (a) just how irrational Menzel could be, particularly about James McDonald, and (b) that Sagan, whom I admired, had an open mind - perhaps a bit too open for some of his peers, if not for ufologists, especially those of a pro-MJ-12, conspiracy-angle bent (see The Demon Haunted World).
Take, for example, Stan Friedman (another guy I admire). In Top Secret / Majic he wrote:
"Another illustration of Carl's misrepresentations about UFOs is this statement in The Demon Haunted World: 'There are reliably reported cases that are unexotic, and exotic cases that are unreliable. There are no cases - despite well over a million UFO reports since 1947 - in which something so strange that it could only be an extraterrestrial spacecraft is reported so reliably that misapprehension, hoax or hallucination can be reliably excluded.'"
So, out of this selection, what did Stan choose to focus on?
"That the truth is exactly opposite is borne out by the Air Force's own Project Blue Book Special Report 14. This report, which evaluated 3,201 UFO sightings, categorized the sightings as 'knowns,' 'inknowns,' and 'insufficient information.' Unknown was defined as 'Those reports of sightings wherein the description of the object and its maneuvers could not be fitted to the pattern of any known object or phenomenon.' It also rated the quality of each sighting, from 'excellent' to 'poor.' The number of unknowns - 689 - represented 21.5 percent of all the sightings evaluated. And of the 308 sightings considered 'excellent,' more than 35 percent - 108 - were deemed to be unknowns. The better the quality of the sighting, the more likely it is to be listed as 'unknown.' Clearly, there are many reliably reported 'exotic' cases."
Stan chose to focus on the part of Sagan's statement that was the easiest to attack, without addressing the very pertinent point raised by Sagan - that there had been nothing reported that was so strange that it "could only be an extraterrestrial spacecraft."
Unless you happen to be a proponent of the ETH, this is not an unreasonable conclusion. It is certainly not the conclusion of a debunker, like Menzel. It is "reasoned," and "balanced" (two words the most rabid of the pro-ETH proponents sometimes view the same way that vampires treat holy water).
From Sagan's writings, I always got the feeling that he was open to the possibility of the ETH being valid, but had set the evidential bar higher than those who accepted that the ETH had already been proved beyond a reasonable doubt.
I suspect that if the pro-ETH types had been a bit more cautious in their conclusions - offering something like "the evidence clearly proves that some UFO cases, with reliable witnesses, remain unexplained, even after the best efforts of investigators to prove otherwise; further, the possibility that UFOs are extraterrestrial spacecraft cannot be ruled out, although it has yet to be established as fact" - they might have found common ground with people like Carl Sagan.
Ufology would probably be better off today as a result, for a whole host of reasons.