Nothing in your reply now, nor in any of your other comments, supports that claim. Your claim does not follow from the fact that in rare, exceptional cases rule-breaking, perhaps in secret, is what an agent has most reason to do according to act utilitarianism, a well-known feature of the view. The act utilitarian reasons to be honest, not defect and so on are on philosophical reflection instrumental to the core utilitarian goal but such virtues, once habitualized, are nonetheless real features of the utilitarian person's psychology just like in other people.
Do you possess any empirical evidence showing that real world utilitarian adherents are less upholding of everyday norms against lying, stealing, and so on? In my experience real world utilitarians (I've known a bunch of them so far in life) tend to be overrepresented in working for or donating to effective charities or organizations that work to eradicate global health problems, poverty and factory farming and at the same time no less conscientious with regard to common sense norms about honesty, keeping your word, not stealing and so on.
You haven't described what alternative moral view you yourself adhere to. Does it have an absolute prohibition against secret rule-breaking? If the only way to prevent the end of the world and the death of everyone would be to secretly break some everyday rule once then you'd think your obligation in the case is to let the world end? If not then we have identified a case where your own moral view promotes secret rule-breaking. Would that warrant saying that your own view obligates you to have a "fundamentally untrustworthy and conspiratorial mindset"? If not, why not?
