We would be even more foolish to think that we, ourselves, are not susceptible to deception.
The moment I believe that I cannot be deceived is probably the moment that I am being deceived. The scriptures are filled with examples of that kind of warning to not be deceived.
Who is Jesus speaking to when he warns about the coming deception (Matthew 24:4-5)? Who is Paul speaking to when he warns about deception (Galatians 6:7, Acts 20:29-30)?
They're both speaking to believers, those who believe that Jesus is, at the very least the Lord, and many times they believe He is Christ, yet apart from Him they can do nothing, and therefore they (we) can be deceived if we take our eyes or dependence off of our Lord, Jesus Christ.