That's Humpty Dumpty thinking. You can interpret the words however you like, but effective communication requires some sort of agreement about definitions. For most people, and in dictionaries, "genocide" specifically does not mean "lots of people", no matter how you personally choose to interpret it.

http://en.wikipedia.org/wiki/Genocide :

    "the deliberate and systematic destruction, in whole or
    in part, of an ethnic, racial, religious, or national group"

http://www.ushmm.org/wlc/en/article.php?ModuleId=10007043 :

    It is a very specific term, referring to violent crimes
    committed against groups with the intent to destroy
    the existence of the group.

By all means interpret it differently, just don't expect to communicate effectively.

(And yes, I know that "decimate" used to mean "kill one in ten" and now people use it to mean "kill nearly everyone". I know language changes, but "genocide" is still rather specific, and has not, to my knowledge, broadly changed in the way you intimate.)