this isn't hard from first principals.
the state has a limited monopoly on violence / use of force as part of the rule of law. they have both an explicit and implicit authority to use or threaten force accordingly in order to (literally) enforce the law.
those who willingly break the law are aggressors against the law, against the legal order, and therefore by extension against the state and the people that the state is responsible to protect. the number of aggressors and whether or not they are armed does not alter this fact. absent direct and immediate personal danger, only the state may respond lawfully. therefore they are obligated to do so - or rule of law will begin to collapse. failure to respond would be a moral failure on the part of the state.
the armed status, nature of offense, and intent behind the offense should determine the scale and character of the state's response, but it has no bearing whatsoever on the justice of the state responding in and of itself.
a mass challenge and breach of the border of a sovereign state must be handled immediately, and the only means to do so is violence - either threatened or used. the choice and nature of that violence is dowstream of the aggressor's actions.
sapper's appeal here seems to be against the use of force in and of itself, on the grounds that the aggressors are (ostensibly) unarmed. this is a logical error. the state's authority depends on its ability to compel compliance with the law. denying lawful recourse to force negates the state's raison d'etre. the aggressors being armed or not, violent or not, compliant when challenged or not, are relevant to to the nature and proportionality of the response, but not to the legitimacy of enforcement itself.
based on that, the original question in the OP has not been answered. force is fundamentally required to enforce a border at all. the question is the nature and degree of for that would be a proportional response to a mass incursion - given that such a response is to both prevent this incursion, and deter future such incursions.