You're providing a large corporation with a direct line of communication inside your home --- one that you have absolutely no control over.
It's virtually inevitable that they will try to "monetize" this in any way possible --- and not necessarily to your benefit.
Thanks but no thanks.
No ... not like these. I can control any communication through these.
You have no knowledge or control over Amazon's communication with the "smart speaker" in your home.
How do you control what other people say to you through emails they send you to your Gmail account?
I get the point you tried to make: Alexa is a listening device customers intentionally plant in their home. But if you do care about corporations listening in, you're missing the forest for the trees. Gmail alone is far more incidious and has the potential to reach far more personal information than Alexa.
But even if I had a Gmail account, it would take some time/effort to learn my identity. Buying a smart speaker surrenders your identity and location right off the bat.