So which is it?
"I just know for a FACT that there are no aliens."
or
"I'm just saying what i REALLY and heartely believe! I believe this with all my heart."
?
One is a statement that you ahve evidence that something doesn't exist, which is impossible unless you have data from every planet in the universe (you don't, no one does) and the other is a statement about your feelings on the matter. Feelings and scientific fact are 2 very different things..
Personally, I do not believe little green men are visiting this planet. I do, however, believe that it is the pinnacle of arrogance to believe Earth is the only planet with life on it in this great big universe. They're out there, living their little lives, just like us, wondering if anyone is out there.