Very likely you had read or heard before the terms: religious evangelist, or technology evangelist. These are people that try to inspire, motivate or convert others to their ideas.
Ufology also has such evangelists. We had seen them frequently or heard about them.
But they really are just known armchair experts in steroids and they do exactly what armchair experts do: talk and by doing that they continue the “tradition”, and maybe their hidden goal, of increasing the obfuscation already existing in this field.
These evangelists as a rule never had done systematic and serious atmospheric observations, their agenda always run based on preconceptions and the exploitation of some sightings reports.
Some of them promote the self contradictory ultimate goal of “disclosure” and the idea of coverups. Many times these evangelists are embedded or are intrinsic part of the businesses that nurture and exploit the UFO/ET religion, the congress, conferences, publishers, documentaries, movies, etc. All these businesses have a vested interest in the perpetuation of the myths, conspiracy theories and obfuscation in general, solving any issues is far from being any of their goals.
But we know exactly how these people that talk frequently of coverups will reject any idea of reality that do not conform to their preconceived ideas of reality.
In a very specific sense these Ufology evangelists are trying to spread the “nuts and bolts UFO/ET religion”, anything that may contradict the precepts of such religion will be belittled or ignored, so in that sense these evangelists will be covering up anything that may hurt their religion, we had seen that multiple times.
An objective and systematic observation of reality is never in these evangelists agendas, as is never in any religious evangelist, and that is really what is needed.