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if you can make the definitions to suite yourself you will never lose a debate.

I'm still waiting for you to define "selfishness". Defining your terms is not a tactic. Every term used in a debate must be clearly defined for the debate to even proceed. Normally, the definition of a word is not controversial as all participants have a common understanding of the term being used. But whenever it becomes apparent that participants are using a term to mean different things, reasonable people of good will will take a moment to negotiate a common definition so that the debate can proceed without confusion.

You have my cancer cell / normal cell metaphore. I think that expresses clearly the distinction that I have in mind regarding self interest versus selfishness. What exactly is your problem with looking at it that way? How do you want to look at "selfishness"?

selfishness is a hijacked word.
It's was originally a synonym for 'looking out for your own self interest'
to use it other wise is 'defining your terms deceptively'

Word history really isn't relevant. (BTW, the word history that I found online does not support your history assertion.) What is relevant is what a word currently means to speakers of the language. Definitions of "selfish" (adjective) found online do not support your assertion:

"(of a person, action, or motive) lacking consideration for others; concerned chiefly with one's own personal profit or pleasure." (Google search)

"devoted to or caring only for oneself; concerned primarily with one's own interests, benefits, welfare, etc., regardless of others. 2. characterized by or manifesting concern or care only for oneself: selfish motives." (dictionary.com)

"1. concerned excessively or exclusively with oneself : seeking or concentrating on one's own advantage, pleasure, or well-being without regard for others 2 : arising from concern with one's own welfare or advantage in disregard of others a selfish act 3 : being an actively replicating repetitive sequence of nucleic acid that serves no known function selfish DNA; also : being genetic material solely concerned with its own replication selfish genes" (https://www.merriam-webster.com/dictionary/selfish)

Word history really isn't relevant
there you go again

Love that quote. But that was so so THEN.

some things never change.