The only effective means courts have to prevent or stop governmental violations of constitutional rights is through injunctions. But injunctions have teeth only when they have the potential of a contempt conviction behind them. In other words, in issuing an injunction, a court is saying, “stop doing that or else.” The “or else” is a criminal conviction for contempt, leading to a fine, imprisonment or both. Absent the “or else,” the injunction is all but meaningless.
But if the president signals to government agents that there exists the likelihood of a pardon when they violate a judicial injunction that blocks his policies, he can all too easily circumvent the only effective means of enforcing constitutional restrictions on his behavior. Indeed, the president could even secretly promise a pardon to agents if they undertake illegal activity he desires.