The notion of a police presence at all, though, at a paid-for exhibition booth for petition signing is at best dubious and at worst...potentially criminal.
The notion of 'authorization' is undoubtedly a straw man; either the civic center took the money or it did not. Either the booth's activities were consonant with whatever ''exhibitor's code'' was in force or they were not. However, pls note that both these conditions were known in advance to the civic center (or, at minimum, should have been known, were the civic center authorities even marginally competent), and the notion of posteriori invalidating the exhibitor's activities stinks to high Heaven. To claim, after the fact, that the exhibitors represented that they intended to do actions A, B, and C, but actually engaged in doing actions X, Y, and Z, where X, Y, and Z were violations of some sort, sounds both tinny and flat to my (admittedly somewhat cynical) ear.
Why, again, were the police there in the first place? What crime was alleged and by whom?
I'm finding it impossible to believe (to paraphrase you) that a petition-gathering group in an exhibition booth (as opposed to, say, obnoxiously button-holing passers-by a la the Hare Krishna types) constituted such a serious threat to public safety that five officers' presence was required. This simply doesn't pass the smell test.
This was apparently in the parking lot of what is no doubt a largely publicly financed center, so I'm not surprised that a significant police presence would be routine. And it's quite possible that there is a chronic problem with unauthorized groups setting up petition-soliciting and/or information-distributing booths, thinking that it is a "public" place and therefore freely available for such activites. If this were allowed, it would obviously severely undermine the ability of groups renting the center to offset their costs by selling rights to put up such booths. That's why my best guess is that the officers were originally led to believe that the group lacked official permission to be there, and perhaps the people staffing the booth quickly mounted resistance to the officers, before providing any evidence that they did in fact have a right to be there. I find the articles' (there are 2 slightly different versions on the linked website) fuzziness about the chronology of events to be a bit suspicious -- seems deliberately vague about whether the officers continued any actions against the group after being told by PK and/or center officials that the group was authorized. I'm always of suspicious of people who make loud accusations while being fuzzy with key facts.
That said, it's pretty clear that the officers did engage in some inappropriate and unprofessional actions. The kissing picture alone fits that bill, especially given that it occurred while a group that would clearly object to it was renting the center, and in front of an authorized booth whose staffers would also clearly object to it (perhaps if the officers had jokingly done this while a gay group was renting the center, it could be written off as good-natured kidding around). I'm sure these officers are going to have some 'splainin' to do back at the precinct house (and I suspect that if a breathalyzer test had been administered to them on the spot, the results would have been "revealing"). But I'm not convinced that their actions were as egregious as the articles are painting them.
The booth-operators, and the like-minded publication which carried this article, clearly have a vested interest in revving up and mobilizing all their potential supporters, given that they have a limited time in which to obtain a significant number of signatures, so they certainly have motivation to exaggerate. It's not clear what benefits -- personal or political -- the officers could possibly have imagined coming from the actions which they are alleged to have committed, or even from the lesser actions which they clearly did commit (but again, I rather suspect that a breathalyzer could have shed some light on the nature of their reasoning processes).
It's not clear whether the booth-operators bought their rights from the civic center or from the Promise Keepers. It may well have been the latter, if booth-renting rights are part of the overall rental package (as is usually the case with this sort of venue). E.g. when a gun show operator rents a civic center or fair grounds, they are entitled to control what booths operate on the property -- both for-profit and non-profit. This is often a major source of revenue for many organizations that put on big events like this, and booth rights are often linked to larger sponsorship packages, and large sponsorship packages often include a guarantee that no competitors will be allowed to exhibit or sell at the event. And when you've got one entity that owns and operates a venue on a permanent basis, and another entity that is renting the venue for a brief period along with specified but not unlimited rights to use it, administrative foul-ups are not uncommon. However, even if that was at the root of this incident, police officers are duty-bound to handle conflicts in a professional manner, and to firmly refrain from taking actions which would escalate conflicts.