"I don't feel the existence of trans women diminishes my identity or takes anything away from me."
Their existence doesn't change anything for you, I agree.
The proposed changes in law which mean, in effect, that there will be no such thing as female-only spaces/support groups/hospital rooms etc will change a lot for you and for other women. Maybe you won't notice it until you or someone you know well are gravely affected by these changes, but they will.
Even if you're alright Jack, these changes whereby "a woman is anyone who says they are" will negatively affect millions of women whose statistics will be skewed, who will have to share a prison cell with a male who likes to use his penis recreationally, who will have to get her smear test from a man in makeup because it will be bigotry and against the law to say "No, I don't want a male sticking his hands up my fanjo".
Even if you're alright Jack, you must care about other women at least a bare minimum in order to call yourself a feminist.