Is Yahoo Reference: Thesaurus biased?

I can not resist making this my first blog post.

While trying to create an interesting blog name, by looking up words at the yahoo reference website, I was a bit ticked-off after reading what they had in their thesaurus describing the word "conservative"

I have copied and pasted below:

CONSERVATIVE

adjective

• Strongly favoring retention of the existing order: orthodox, right, rightist, right-wing, Tory, traditionalist, traditionalistic. See keep
• Kept within sensible limits: discreet, moderate, reasonable, restrained, temperate. See plain, restraint
• 
  
• Clinging to obsolete ideas: backward, reactionary, unprogressive. See politics
• 
  
• Able to preserve: preservative, protective. See help
  

noun

• One who strongly favors retention of the existing order: orthodox, rightist, right-winger, Tory, traditionalist. See keep

The thesaurus comes across as slanted.... to be a political conservative means to be "clinging to obsolete ideas", "backward", "reactionary", and "unprogressive"?

Well, some say our history books are being re-written to push a liberal / "progressive" agenda.  It looks as though the thesaurus, and maybe even some dictionaries, are pushing that same agenda?

Any thoughts?