Earlier quoted context omitted.
To me it's pretty simple. If you don't like what Google is doing, don't use their services, and don't buy their products.
But as mentioned above, if you don't want Google to potentially track your behaviour and preferences, "don't use their services" encompasses "don't send email to anyone with a gmail address".
If i'm on gmail, then you need to talk to gmail to talk to me. It's a tradeoff you'll need to make. If you want you can GPG encrypt the email, but there is nothing from stopping me (legally, morally, or otherwise) from just decrypting it and replying with the contents, or saving the decrypted message in my google drive.