Graffiti which is art, and notably graffiti which is made with the owner's/authority's consent (which may be implied), is not a destruction therefore it's not violence.
It can even separate from the right of ownership on the building and be a different ownership which includes the intellectual property rights of the creator. Bansky can sue you if you destroy his graffiti. But he may have to compensate the owners in the case that he deprived them from the absolute right of disposing their things as they wish.
Regarding graffiti as statement for a universally accepted cause (peace) and targeted to a publicly funded building: yes, it still is considered as destruction and therefore a form of violence. But that is not the case. A destruction can be accepted if you change your approach to it. It is even legal if in that way you defend the law (for example making graffiti on the infrastructures of an occupation army is consistent with your country's legal demand for defense etc).
But I am not sure what do you mean by destruction. It seems that you like graffiti and that word does not reconcile to your taste and your anti-violence perceptions. In general and in metaphysic way every destruction is violence. But in practice there are levels on every quality of every thing, the point is to know why you act and be consistent with your whole perceptions.