The issue is that I don't think it is the most effective argument for influencing others to change their mind.

Why? Because people assume that it is highly unlikely that they will be the target of such a search, assume that a warrant would be needed, and in the bigger scheme of things, a backdoor is worth having in case someone who has committed a crime or is reasonably suspected of having committed a crime can be pursued.

So there's a principles / practicality tradeoff that I think people are making.

Further, telling people that the government might spy on you with the purpose of locking you up or fining you comes across as overly paranoid. Again, not saying this hasn't happened in the past or in other regimes, but this just isn't a sizable number of people's experience (in the US or Canada for example).