I've had this conversation before. The consensus last time was that I should tell every single person on my contacts list to download Signal if they want to stay in touch and if they refuse it means they're shitty people that don't care about me but I'm totally not a shitty person for forcing my preferences onto others.

People don't realize that in most of Europe WhatsApp is more popular than iMessages are in the US. Not having WhatsApp means you're not texting to anyone.