Jim Crow Laws

After reading this article, I'm both in shock and I'm confused. I don't understand how they could've prevented Blacks from having equal rights such as voting after the civil war. How could they have thought it was constitutional to impose these "Jim Crow" laws on Blacks? Also, it's ridiculous that police and lawyers and judges would approve of lynchings like that, and yet Blacks couldn't fight back because they'd be punished for that! I can't imagine what it would be like today if they hadn't done the Civil Rights movement in the 60s.