Things believed by 30-45% of the population are not really "fringe beliefs." And I doubt that recent events are driving those numbers down! Though I'd agree that it is likely that most of the people believing these things do so casually, and do not think much about them as they go about their lives.
That's the thing, though. Except for a small group of people, belief (or possible belief) in alien visitations doesn't affect their lives. They're not afraid, and frankly, they're not even that curious about it. They're just thinking: "Yeah, I'm sure the government knows more than they're telling us, and space aliens visiting Earth seems like a reasonable idea."
But these people have real issues to worry about, and researching UFO reports isn't one of them. It's important to remember that many people know very little about space, astronomy, and the universe. A friend of mine was once asked by a taxi driver, "How do satellites manage to avoid the stars when traveling across the sky?" The driver was otherwise quite a clever man, but he just didn't give a rat's ass about space.
And for someone with that little interest in astronomy, it's easy to assume that interstellar travel isn't such a big issue. This is where scientists and government officials should step in. Sadly, however, it's the sensational claims that get the attention, making it appear as though it's a widely accepted belief among scientists and governments that extraterrestrials are visiting our planet. But empty vessels make the most noise, and no tabloid newspaper wants to publish an astronomer explaining why distance and time are such formidable obstacles. And debunkers are the boring people who are always ruining the fun.
It's no wonder that quite a few people would answer yes when asked whether aliens are visiting Earth. They read about it in some article, they haven't really thought about it, but spontaneously they say yes. That does not mean, however, that 40 percent of the population are potential paranormal investigators prepared to move into the annex at Skinwalker Ranch.