I must (and it is a personal "must") agree with blssdwlf.
There is room for both (or all) approaches, of course. But for me, I have an emotional and life-experience attachment to the original series and ship. It pulled me in and opened up new possibilities when I saw the very first episode the very first time it aired. That is canon for me. When other series or movies depart from that, I recoil and cringe. It is actually very visceral (no examples named so as not to derail things.
My point is 1) my canon is like blssdwlf and it is an emotional decision for me, and 2) it simplifies my universe to allow me to enjoy what I like best about it.
Life is full and good, but I cannot take it all it. I must limit my scope.