I'm in chapter six and therefore trying to tie up loose ends around the map to get my full money's worth from this game. Lots of people in here talk about killing various dragons - but so far I haven't HAD to kill any one of them. (I know I would have needed the Silver's blood to make that Human Sick armour).
My question is........Are there conversations/quests that send you to kill these dragons, or is it something that all you cool people just do for the sake of it? I will kill at least one before I finish the game, but I dont like to do things that could later deprive me of a quest. Please help

The red dragon you just talk to and tell him that you shall kill him.

The shadow dragon you simply talk to and he attacks.

The silver daragon i dont know where is.

Don't worry, you'll have plenty of opportunities to kill dragons...they'll find you some way or another. The only two 'optional' ones which are part of side quests are Umar Hills and Windspear Hills. All others are part of the plot.

You also have to kill a Black Dragon somewhere in... argh... Suldesellenar? Bah, I hate that stupid city anyway.