We should not pay for the wedding but the security should be funded by the taxpayer.
Every person in this country should be safe whether it is Jo Bloggs down the street or in this case the Royals. If the police perceive a greater risk of a terrorism attack which could harm both people in the streets watching or the Royals themselves then they should deal with it.
Now most of the police who are providing security to this event would be doing other duties and so the 2 million is not the net cost, the net cost will be less than this to the tax payer.
Even if the police manage this event by giving a lot of overtime (inflating the income of certain police officers) or have to hire outside security firms, think of the effect on the economy.
Firstly this extra income that these officers earn will be taxed - so a substantial amount will come back into the coffers of the government and so this part will not be paid by the tax-payer.
Then the recipients of this extra income have to decide whether to spend it or save it. If they spend it, then businesses make more profits etc and these then also get taxed and so on..... The effect on the tax-payer is not nearly the level of 2 million that is banded about by the press who are only wanting to provide a controversy to get more readers and therefore more advertising revenue.