I tend to just keep it light, as not a ton of my friends care enough to put the slightest bit of energy into such things. I just tell them it IS whatsapp, but blue instead of green and that everything else surface level is the same. If they entertain me a little i then explain simle things like how whatsapp puts media in your phone without opening the message (they can check that in their gallery for themselves), and that signal doesn’t. Once they realise that any seedy thing thats sent to them can be seen by any other app with permission to the gallery they are for sure more inclined to install it and consider other simple alternatives
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