Everyone has the right to protest and this is not a general election which hasn't gone the way you had hoped. At least in that circumstance things can change after five years.
This decision will effect us, our children, grandchildren and all future generations. As such it is not something I can accept without making my voice heard loud and clear.
And I think, speaking as a non British resident, that immigrants (whether they are from the EU or not) need a symbol of reassurance that they are not hated and resented by the majority of the population. This is a good way to do it.
As for it leading to anarchy - excuse me but is that supposed to be a joke?