Hi YumYum
I will attempt to explain both the "Fool" thing, and the bears thing.
In Mathew 5:21-24, Jesus begins by saying:
"You have heard that it was said to those of old, 'You shall not murder; and whoever murders will be liable to judgment.'
He is quoting what their rabbis were teaching them - partly based on the Jewish law covenant, but partly with extra burdens placed upon the people by the scribes and Pharisees.
Jesus then focused on relationships with their Jewish brothers: ""But I say to you that everyone who is angry with his brother will be liable to judgment."
He then escalates with increasing levels of insult and judgment - "Raca" (often translated simply as an "insult") was actually a very strong Jewish insult - this would be liable to the Sanhedrin (the Jewish religious high court), and "Fool!" to the fiery Gehenna.
Jesus' point, in the context of the comment about murder, was that you didn't need to actually, physically MURDER someone to receive judgment - the Law was supposed to be, in spirit, about a Jews relationship with his fellow Jew, and that holding their brother in contempt was like murdering him!
However, the relationship the Jews were to have with Jesus was spelled out just before he condemns the Pharisees. He says, in the context of religious titles:
"But you are not to be called rabbi, for you have one teacher, and you are all brothers." (Mathew 23:8)
Jesus was their teacher (or rabbi), they were brothers. Like the US Constitution, the issue here is about separation of powers.
As creator, God has the right to both give and take away life, but humans do not - unless those rights have been granted to them by God.
It is not about "do as I say, not as I do" because none of us are God! There is no equivalence between us and God, so it's not double standards if God tells US not to do something, yet does it himself - just as we personally might not be allowed under law to put a criminal to death, but our State may be able to. It is about separation of powers.
Individually, we are not equivalent to the State... and neither are we equivalent to God.
Jesus, on the other hand, was supposed to be the Son of God. Therefore he did have the authority to condemn the Pharisees in the way that he did. Jesus was condemning the religious authorities in his authority as Son of God.
However, in Mathew 5 he is talking about relationships with our brothers (or more specifically, Jewish relations with their Jewish brothers). Big difference.
As to the bears incident, all translations miss the underlying Hebrew, which is that these were not chidren. The original Hebrew ("neurim qetannim") should be translated "young men". In Jewish law, a "young man" was anybody under 30 years of age.
So here was Elisha facing a group of at least 42 young men - not children - who were insulting him. That could be viewed as a GANG! It is quite possible that Elisha's life was in danger, which is why he cursed them.
Even though the bears devouring 42 of their number might still sound like a harsh response - it may have set an example for others to show more respect to their elders, especially a prophet. But either way, these were not mere children. For whatever reason, the translators have done a poor job with this passage.