This question and its accompanying blurb are unfair to younger siblings who aren't selfish and arrogant. As a former English teacher, I generally see no reason to make sweeping statements or use hyperbole. If your own siblings are as you describe, that is a problem with them, not with all younger siblings.
I am the older of two siblings, and I can safely say that neither of us is selfish or unkind. Our mother impressed on us the importance of loving each other and looking out for people we love. Are we perfect? No. Do we both suffer from depressive disorders and hereditary physical problems (high BP, mainly)? Yes.
But my brother is the one who went to bat for me when my stepfather persisted in touching me inappropriately. My brother is the one who assured me, "If you ever marry or date a guy who hits you, you tell me, 'cause I'm going to hit him." My brother is the one who affirms me and tells me he likes me just the way I am.
My brother works almost 40 hours per week cleaning bathrooms to help support his family.
My brother is my closest friend, and he considers me his. He knows and understands me better than anyone else does, because he's actually tried.
It is perfectly all right to be angry with your own siblings, or feel that you got the short end of the stick. But please don't use such a broad brush to paint younger siblings.