Here lies the root of our disagreement (emphasis mine):
I contend that none of the things you listed violate secure communications in the described scenario (using a GV number for Signal).
By registering, you will have to agree to their ToS
Does not affect security.
Allow them to collect everything they can about you, including your IP, browser fingerprint and so on
Might affect privacy, but not security. (But there are privacy tools and strategies that can mitigate this.)
With whom you speak and how often
Since you’ll be using Signal, they won’t get this.
You will show them your support (which you shouldn’t; Google is not exactly a good company respecting its users).
This also doesn’t affect security.
While I’m inclined to agree about lack of respect for users’ privacy, it’s debatable whether using them as a piece of distrusted infrastructure shows them our support. (It depends on how exactly we define “showing them our support.”)
Also, remember that I actually wrote:
I never said it had to be from Google. If you can find a better alternative, by all means.