Regarding security, imagine something happened in that church, a bomb or a nut with a machine gun, for example. The monarch, and the next three in line to the throne were in attendance. Just in terms of lineage there, that would be a disaster. Then you have the actual human cost of it all
Imagine a police officer guarding parliament being killed because he didn't have any property safety equipment on to defend himself against a knife attack. Just happened this year.
Imagine prison officers being told they face being killed any day because they are so outnumbered by prisoners who have remarkable access to drugs, phones and weapons. Happens every day.
Imagine ordinary law abiding citizens being burgled, raped, mugged or attacked while no timely or appropriate response is given by the police because they are so understaffed.
Imagine your parent waiting hours for an ambulance while lying on the pavement having a heart attack - because there is such a shortage of ambulance crews to respond to emergencies.
All lives are equal - the royal family is not entitled to divert resources away from essential public services that benefit us all. A carriage ride round Windsor was an unnecessary and extravagant indulgence, by an extravagant and overindulged family (who can opt out of titles and privilege ant time they choose)