Here is something that I posted once before in a similar thread:-
I am a very, very logical person, and have long been fascinated with this subject.
Here are my thoughts.....
Let us assume for the moment that UFO's are 'aliens'.
I can only logically think of three reasons of why they are visiting us:-
1) they want us to join some sort of 'Galactic Federation'....
2) they want to conquer us, because they want something from this world....
3) they are studying us, out of scientific curiosity.
Lets look at each reason, logically.
1).....We cant even sort out our own problems down here, let alone join some galactic community!
We are just not advanced and stable enough, so this cant be the reason.
2).....They must be far, far more technologically advanced than we are, and if they wanted to conquer us, they would have done so by now.
So this also cannot be the reason.
So this logically leaves us with reason number 3: they are studying us.
Now, we have the whole planet covered with radar and surveillance satellites, looking out for each others weapons and surprise attacks, so we should detect them.
But, as they are so advanced, they may have some sort of radar shield or cloaking device, rendering them invisible, like our relatively primitive stealth aircraft.
Logical conclusion = they are here to study us, and are so advanced that we cant detect them.
So why oh why do they have big flashing red lights on their ships!?! 
(You dont put bright flashing lights on a stealth aircraft!)
Final conclusion = they arent aliens!
