Of course a bank tax is justified. Remember 2008? Remember Lehman?
The financial industry engaged in reckless and unnecessary risks that undermined the safety of the domestic and global economy. The failure of Lehman Brothers plunged the United States into a recession that we are still struggling to claw out of.
No bank executives went to jail, the industry was bailed out, and banking has recovered more quickly than the economy as a whole. Paying a small tax that doesn't even dent industry profits is the least the banks can do to pay back a country that came to their aid in their darkest hour.
No, Obama's 2010 bank tax was not justified, because it was just Obama trying to make the United States less wealthy. Obama believes that the United States has made their wealth from exploiting other nations. He decided to tax the banks to punish them for making money and being capitalist. The banks didn't do anything but lend liberally, which is what Obama wanted them to do ten years ago.