Why is Jesus so harsh?

Bill Lane asked me a great question after church on Sunday. Why is Jesus so harsh in Luke 14:25-27?
Elsewhere the Bible is clear that we should honour our father & mother, that husbands should love their wives as Christ loved the church etc. So why is he blunt to the point of contradiction here?
All the commentators agree that the point he's making is that our love for Jesus should be so great as to make our love for even our families pale by comparison. But why not say that? Why be so blunt?
In John 6:53-58, Jesus is similarly harsh - so much so that the disciples say, 'This is a hard (or 'harsh') teaching. Who can accept it?' And Jesus replies, 'Does this offend you? (lit. 'cause you to stumble')... the Spirit gives life, the flesh counts for nothing. The words I have spoken to you are s/Spirit and they are life.' (v63).
So I think the answer to Bill's question has to be something about the sheer weight of importance of our decision about Jesus. Jesus is speaking about things that are literally a matter of life and death - eternal life and eternal death. And the only deciding factor in this overwhelmingly important issue is our relationship and attitude to Jesus.
In today's world everything is simply a matter of personal preference and of so little consequence - Sony e-reader or Kindle? Spurs or Arsenal? Sainsbury's or Tesco? - and very few people ever have to take decisions that really matter.
If you watched Birdsong last night, you'll have seen how another generation had to make decisions that really did matter - life and death decisions. The main character, Stephen Wraysford, is told by his superior officer that he must take his men down into a tunnel under the German lines. The Germans burst through from their own tunnel. Wraysford is shot and nearly killed.
But we know nothing of important decisions like these. Jesus has to ram home the truth that he alone must be our God if we are to have life. To use the language of John 6, 'What must we do to do the work that God requires?' the people ask, 'The work of God is this: to believe in the one he has sent,' replies Jesus. And belief means uniting ourselves to the Christ who goes to the cross. Or in the words of Luke 14:27, 'Anyone who does not take up his cross and follow me cannot be my disciple.'