Some points worth considering:
1. Being accused of a thing by the authorities does not make the thing fact.
2. Creating moments of chaos and disruption could arguably be seen as furthering the goals of some anarchists. Many insurrectionary anarchists speak of moments of rupture, where day to day functioning of society ceases and conflict creates momentary openings in to a different world. Increasing frequency of disruption tends to grow not only in temporality, but also in what, for lack of a better term coming to mind, I will call boldness. The author AG Schwarz has counterposed this concept of "signals of disorder" to the broken windows theory of policing.
3. Why wouldn't anarchists participate in such actions? During the Anti-WTO protests in Seattle, many not anarchists were swept up in breaking windows, fighting cops, looting. Why wouldn't anarchists get in on the fun?
4. Describing an action as petty is an easy way to dismiss something. Throughout time people who have suffered the brunt of oppression and domination have found small ways to get theirs, to "talk back", to get over. Certainly smashing a window doesn't cause capitalism to magically end (but maybe the next window is the magic one.. we just need to keep smashing!), but it might be something I can do to signal my general dislike of the current situation.