First of all there is only one giant mentioned in the Bible and that was Golieth (sorry i can't spell)
Goliath was not the only giant in the bible. I won't go into mentioning every last one, but I'll say this. There were many giants in the world at one time before the flood. Goliath, believe it or not, was far from the biggest. Anak was said to be around 150 feet, and he was not the tallest either! Also Anak had three sons. People seem to think that God destroyed and killed innocent men, women and children. He destroyed giants; after many thousands of years, the earth was infested by giants. He was destroying the giants and their followers. After the flood, God had Joshua destroy Jericho, one of the twelve tribes sent by Joshua to spy Canaan took care of Anak's sons, and then God destroyed Sodom and Gomorra; can you guess why? Oh, and there is nothing absurd about giants after the flood. Though it was the 200 Angels (Watchers) who mated with the women, Satan and the fallen have tried to protect them; he of course failed. I have a ton of facts regarding these things, but it would be way too much to list here. But for more info, read the bible very carefully; it has all the answers.