We saw that Devavrata was termed Bheeshma because of the terrible vow he undertook to see his father happy.
Now - a lot has been said in praises of Bheeshma, and his selfless devotion to his father and the nation. Also, a lot has been said against Dhritrashtra, and how his blind love for his son caused the cruel war of Mahabharata. But - please consider this - while they are different in the sense of being selfless and selfish respectively, Bheeshma is more responsible than Dhritrashtra for the tragedy!!!! While he was worthy of praise and appreciation for his selfless love for his father, it needs to be remembered that he had been taught dharma by heavenly gurus, and he knew that the good of a person (even if it one's beloved father) should never be placed before the good of the nation! He should have realized before making a blind promise that, the person who is so greedy and demanding as Dasaraj ( - Satyavati's Father) may very well affect or influence the future generations' thinking, either through genetics or through ill advice!
He also knew that he himself was a good candidate - fit to inherit the kingdom - and he had no right to give away the position as a gift to his unborn half brother - who - at the time was an unknown factor. For all Bheeshma knew, the son of Satyavati might have grown up into a villanous character like Ravana or Kamsa - and he undertook an oath to protect such an unknown character to the best of his abilities -just to fulfill his father's blind sexual desire for Satyavati - who was not even enough in love with Shantanu to oppose her father's unappropriate and greedy demands!!! Being a knowledgeable person, he should have thought of pros and cons before making such a promise. And, having made the first folly - he multiplied it later on by supporting all the wrong doings of Dhritrashtra!!! Hence, the selfless son became the selfish yuvaraja who endangered the nation's well being for his selfish desire to see his own father happy!!.......