Be Fair to Historical Figures?

These days we judge historical figures very freely.  As a failed historian of an older generation, I get queasy with many of the judgments.  Too often they're made by applying current standards to the past, without allowing for the everyday realities people faced.

What are valid standards:

• certainly we can criticize person A when comparable figures at the same time thought, wrote, and acted differently. The issue then becomes what's "comparable"? If Martin Luther King worked for integration as an activist, can we say all politicians, either holding or seeking office, were morally lacking if they did not work for integration?  LBJ worked for integration, but not as soon or fast or strong as MLK wanted.  Do we judge LBJ against MLK or against JFK or Ike or Nixon? 
• there's another standard which can be applied.  I get this one from  a professor's lecture  on Jackson at Readex: if Indian removal was wrong, what was right, what was the alternative?

In some cases I know the answer is tragic, the conflict is irreconcilable.