People who doesn't believe in alien existence are in these 2 cases:
1)Fear them
2)Too much selfesteem.
Um what. Where is your logic in this? Not beliving in something wont stop people from fearing them. People fear many things that do not exists god, satan, ghosts, the boogie man etc.
I will just ask this question:
Prove me that we are the only humanoids in this galaxy.
No alien stuff, just prove me we are the only smart intelligence that is been able to build computer and internet.
Can you prove that we are not? No.