It is. The person you're replying to was naïve, and still is.
It's true: Adding stuff to Wikipedia or OSM can help bad guys get information, and this can have negative effects for you. But the person you're replying to assumes naïvely that this is perceiptibly worse than the negative effects of bad luck. You're going to have bad luck in your life, that's in the nature of luck.
I added the location of a specialist shop that sells mostly grappa. Someone might find that shop with the information I added, buy and drink too much grappa, drive a car and drive over me. It could happen. But thinking that this is perceptibly worse for me than if I hadn't added that location is naïve.
Similarly, your country could introduce a retroactive law prohibiting proxies or introducing some form of liability, and when the Iranians send a list of IP addresses your country gaols you. It could happen, but is it probable enough to be compared to the effects of bad luck on your future life?
If by secure you mean the messages cannot be intercepted, yes Signal is theoretically secure as the process of communication is encrypted. On the other hand, Signal can be blocked as it is not truly distributed and requires a Signal server. Very simply put, blocking the Signal server disables the Signal network. That's why Signal is asking someone to setup a proxy server on their hardware that can then allow certain users to connect again to their Signal servers, via the proxy.
Note that these proxies too can be identified and blocked.
Worse, their IP address could be used to identify you in any investigation. This was the legal risk I was pointing out as you do not know how Signal will use your infrastructure (in ways that may make you liable for something in your own country) or how other countries may become hostile towards you for allowing Signal to circumvent their laws.
