Generally speaking, to make an arrest, one must have probable cause to believe that a crime has been committed. When a protester disrupts some event, that arrest is made, to end the disruption and prevent the heckler from vetoing the event. Frequently, a prosecution for some minor criminal offense, like disrupting the peace follows, and if no effort is made to convict the individual of a crime, a civil rights action will frequently follow and the law enforcement officer defending the civil rights action, in a case within a case, will have to demonstrate that there was probable cause to conclude that the person arrested did commit a crime but that the law enforcement official and/or prosecutor exercised prosecutorial discretion to refrain to pressing charges to the benefit of the protester.
In general, once the arrest has been made the authorities are probably quite happy that this temporary solution has solve the temporary problem of an individual being disruptive and preventing others from carrying on their lawful business with relative peace. The prosecution that follows often has little value to the jurisdiction prosecuting it other than preventing later civil rights suits, and adds considerably to the cost of managing the situation for the authorities, who must file legal papers, book the suspect and detain that person for some period of time, arrange a hearing, summon witnesses, and face the potential embarrassment of mismanagement of those low priority prosecutions leading to acquittals due to poor litigation methods, or due to a weak case on the charge selected as the basis for the arrest, or due to jury nullification. The analysis of any punishment to be imposed and any crime for which a conviction must be entered in a protest case must undergo strict scrutiny to determine if free speech rights of the protesters have been violated.
The high risk of a potential personal lawsuit by someone with a lawyer who knows what they're talking about being brought against a law enforcement officers in a protest situation also can give the situation high stakes for the law enforcement officers that can engender insecurity and fear in the law enforcement officer that may come up in the form of the very kind of brutality by police that can give rise to civil liability.
Of course, an arrest record, minor criminal conviction, the hassle of participating in court proceedings that could lead to satellite legal problems like arrests for violations of bond conditions or failure to appear at a hearing, and so on, are no great gift to the protesters, and will inspire some to use the pending criminal proceedings as a soapbox to further spread their message.
Should there be a lower stakes option for all involved? What if law enforcement officers had the authority to temporarily detain someone for the duration of an event (up to six hours, perhaps) at which they were being disruptive and could then release that person without charge knowing that in that situation any exposure to civil liability would be minimal, even if the act taken didn't necessarily rise to the level of the kind of crime that is ordinarily prosecuted. A temporary detention of this kind would carry with it knowledge on the part of the person detained that it would not produce an arrest record, a criminal prosecution, a potential fine, court costs, or incarceration beyond the immediate detention, the need to high a lawyer to deal with the charges or their collateral effects, or the need to post a bond or appear later at a hearing. The low level of inconvenience and harm imposed on the protester and ephemeral nature of the action would prevent it from turning the protester into a martyr or providing an big soapbox of injustice to harangue against. It would be the governmental equivalent of being bounced from a bar or movie theater, for which the civil remedy is typically the foregone value of the cover charge or ticket to get in, and no more.
Indeed, perhaps it could simply be a codified version of bouncing someone using non-deadly force, with the sole justification required being that it was the desire of the person in control of the premises that the protester not be permitted to stay there any more (which could be presumed if there was no evidence of permission to be there and the person with the right to control the premises was not present), even if they had a revocable license to be lawfully present there.
One could imagine a "tort reform" style dollar cap on suits arising from a bouncing incident equal to say $1000 plus out of pocket lost access fee to the premises and damage to property unless serious bodily injury resulted, with attorneys' fees limited to no more than the award of damages in the case if the bounce was shown to fail to meet even the minimum standards required for one, and a rule giving individuals immunity from liability in those cases with only their employer having legal responsibility.
The point would be to take approaches that minimize the stakes rather than escalate the situation for all involved. The protester might be bounced. A lawsuit against the individual carrying out the bouncing generally wouldn't happen in the absence of serious bodily injury or an excessive period of detention. The rowdy moment normally wouldn't have long term consequences for anyone, however, and protesters knowing that they could make a rowdy protest statement and even get arrested without long term consequences would have an incentive not to go further than that which is eroded if a protester who crosses the line knows that he or she will get a criminal record and have to be involved in the criminal justice process anyway.