God charges Hananiah with causing the people to trust in a lie, as well as inciting rebellion against Him. His transgressions were so grievous that God killed Hananiah two months later—a month for each year in his false vision (Jeremiah 28:1-4).
Hananiah's prophecy urged rebellion against God in a couple of ways. First, Scripture is clear that God had installed Nebuchadnezzar in a position of power over this area of the world. Though not a godly man, he filled a position that God had given him, thus to resist his rule was to rebel against the God-ordained order. When Hananiah predicted deliverance in just two years, it encouraged Judeans to think that they did not have to submit to this foreign king. In this way, he encouraged them to disregard God-instituted authority.
Second, Hananiah's lie subtly altered the reason for their crisis. He redefined the foreign domination from something that God deliberately caused (as told by the prophets) into something that He merely allowed and would soon remedy. The false prophet shifted the explanation of their pitiful circumstances from something that God had orchestrated due to the sins of His people into a time-and-chance problem that He would reverse.
This removed any need for self-examination. It exonerated the nation and its leaders, removing any thought that the people had misbehaved themselves into this crisis by rejecting God. By eliminating any thought of cause-and-effect regarding sin, Hananiah was in fact encouraging them to continue in their disobedience. Without any apparent consequences for sin, the mind begins to reason that sin is not the problem. Hananiah told them everything would be fine, but God saw it as teaching His people to rebel.
Something similar is happening today in a small way. Some are promoting an idea that the world is actually getting better. It is not a widespread belief, but some have taken such a rose-colored view of God that they believe mankind's best days are just ahead. They are convinced that there will not be catastrophe and death leading up to Jesus Christ's return.
To arrive at such a notion, one must nullify the pattern of God's prophets, just as Hananiah did. One has to find new meaning even for the words of Jesus Himself in places like the Olivet Prophecy where He plainly says that "unless those days are shortened, no flesh would be saved [alive]" (Matthew 24:22). Under this view, the bulk of Old and New Testament prophecies become either merely symbolic or already fulfilled, including all of Revelation. And a person must really cherry-pick his evidence to maintain the belief that circumstances in the world are improving! Some are actually doing this for the sole purpose of giving hope. However, like Hananiah's prophecy, it is a false hope.