Hardcore nuts and bolts UFO/ET believers are ironically the biggest obstacle in gaining a faster advancement in Ufology and the reasons are multiple but it boils down to a single one: their very narrow preconceptions and their emotional attachment to these preconceptions that make many of them not different than religious fanatics.
It had already been mentioned that they have a very narrow anthropocentric view of the UFO manifestations and that they dismiss and ignore any evidence that do not conform to these narrow preconceptions effectively suppressing evidence that they think do not match their expectations.
Many of them reject the idea that making atmospheric systematic observations can answer any question, but it is obvious that this position is not very consistent even from their point of view simply because they relay heavily in sighting reports and systematic observations are just an organized and controlled way of making these sightings.
But almost anybody making regular atmospheric observations is reporting with extraordinary consistency the presence of anomalous autonomous flying objects. These anomalies can be observed by anybody, there is almost a certainty that anybody making just a little effort and using very affordable instruments will be able to observe them.
Some of these anomalies do actually resemble balloons or foil material, but not all are like that. People with dishonest approach will only mention these anomalies types as a way to dissmiss all of them, but that clearly is intellectual dishonesty. There are multiple cases of anomalies being far from similar to any mundane object, of morphing/polymorphic anomalies, etc. All of that had been clearly documented, any honest approach to this needs to consider all anomalies documented.
But the hardcore nuts and bolts UFO/ET believers almost all the time will dismiss anomalies, the only things in the sky that can be observed unequivocally by almost anyone and the reason again boils down to preconceptions. Anomalies do not conform to their expectations then that reality should be dismissed and suppressed.
By doing that they are actively suppressing the only real thing that can be validated at any level and that very likely is at the core of the UFO dilemma.
That is why they are today the biggest active obstacle in trying to solve the UFO dilemma.