You might be right about some believers - using faith as an excuse not to think. I don't know. I'm not them, and so I am not qualified to tell someone why they believe.
But your premise is untrue for me, and I suspect many others.
I have faith in Christ (and so, God) because I love and trust Him. I love what He did and taught. I believe in what He did and taught. I strive to follow Him, though I come up far short. So if He said He's coming back, then He's coming back. If He believed in God, and called Him Father, and both followed and loved His Father... then I do the same. Because I trust Him.
Some of this is from reading about Him. Some of it is about the evidence I have of Him in my life. The fruits/gifts of the Spirit that my faith in him have granted - peace, forgiveness, understanding, love, prayers and questions answered. Guidance that I can feel, albeit not prove.
I don't rely on faith just because I don't have a better answer, or am too lazy to search for a better answer. Faith in Christ is just a part of me... as natural and present to me as breathing.