As much as Carl Sagan was a big pro-alien life advocate, especially
when it was not supported by many of his colleagues, he was among
the first to explain why Venus was too hot for life (the greenhouse
effect) when others were still holding out for a relatively cool planet
with lots of rain from those clouds and maybe even whole oceans
of liquid water. The Soviets designed their first Venera landers to
be able to float on water, if that gives you any idea how much merit
certain professional groups held on to that idea.

And as for Mars, while others said the changing areas of dark and
light "patches" on the Red Planet were plants growing and dying with
that world's seasons (I remember reading a National Geographic article
on Mars from circa 1954 declaring that astronomers imaged an area of
plant life the size of Texas!), Sagan correctly said it was Martian
surface dust being blown about by the planet's winds.

As for this growing trend of skepticism about no other life - and certainly
no intelligent life - in the Universe, while of course there is scientific
merit to it, I also sense an effort to give humanity one last chance to
be “unique” in an existence that has made us smaller and more insignificant
than ever. We are already microscopic dots compared to the vastness of
the Cosmos, and if it turns out that we aren’t even the only or smartest
creatures around, well then, might as well just chuck it in for humanity.

Not a good attitude to take and certainly one I do not advocate, but
that is how I fear many people think, as after all most of them focus
on the minutae of life on Earth and rarely think about the wider picture
in any serious way. I also know people who grow genuinely afraid of
the idea of an immense Universe where we barely register upon it.