Just a guess, but I would think that a significant motivation for doing a trial is to ensure that the frog is boiled slowly.

Opposition can now be met with "it's just a trial, relax". Then you expand the trial a bit. Keep running it until the discourse moves on. And then a few years down the line, when you roll out the full system and people complain, you can counter with "these people are exaggerating their concerns, we've trialled this for yeaaars and there were very few problems!"