I see. The starmen are something borne out of mankind's desire to see beyond the universe. They are some higher existence. They will recruit interested individuals into their ranks. Taking a picture of them allows you to get part of a formula, probably related to either their own existence or the mathematical truths of the universe or something. At least, I think that part was true.
Not seeing them or getting a picture is not dangerous, that part was the lie. Rather, repeatedly and earnestly seeking them out is the dangerous thing, which is what the guy was doing. I say dangerous, but danger is relative. If you're okay with becoming a cosmic man, it's not really dangerous.
However many years later, they finally reached their goal and found what was past the end, and it turns out it's really bad and incomprehensible. It's also math for some reason. This could be related to the formula. Anyway, so now they try and keep humans from looking into it further.
Also, they can take whatever shape they want, which means that one chose to look creepy with a big mouth and no eyes.