So does Robert Baratheon hate all Targaryens cause of Rhaeger atau is there another reason

His hatred could have started when he watched his parents die (by shipwreck) on returning utama from their failed quest to find a bride for Rhaegar, and Rhaegar stealing Lyanna from him many years later only added fuel to the fire.

Yeah I'm pretty sure he hates the Targaryens just because he thinks Rhaegar kidnapped Lyanna...Even though that seems highly unlikely because Rhaegar is so gallant and honorable...Maybe the clues will start coming together in book 5...Hopefully! If it ever comes out!

I also think fear has something to do with his hatred for the Targaryens. Robert is not the rightful king and as long as there are any Targaryens alive they threaten his crown.

I think he hates the Targaryens because of Rhaegar who kidnapped Lyanna, but also because she died and he made the Targaryens(especially Rhaegar) responsible for that. Maybe because he feels for Ned too, maybe because they were enemies in war. I think everyone should build up his own reasons...