A lot of these types use 'perfect being the enemy of good' as their attack vector. If it's not private and anonymous why bother? If you can't cut out all big tech companies, if you can't stop buying any American goods, if you can't feed all the poor or house all the homeless, etc. It's an effective way to attack progression by making people believe they should just stop fighting, they'll never win. You nailed it, Signal is private, it doesn't claim to be anything else.