I'm on the fence.
IMO the ethics are not clear cut.
Courier services and post people are delivering without breaking social distance.
Businesses would in some cases go bankrupt and / or employees would lose jobs without customers.
Delivery drivers are often self employed and paid per parcel.
A lot of people on very low wages have no savings won't make ends meet on a reduced furlough wage or if their company goes under.
A lot of high street businesses have creatively problem solved and started selling online locally and obviously want/ need custom.
On the other hand
Some businesses are not ensuring safe working environments including maintaining distance between employees or are not sympathetic to employees from households where someone else is shielding.
Some people working in warehouses and delivery would rather be furloughed due to childcare or similar reasons.
Deliveries mean more traffic on the roads, slightly increasing the odds of an accident (which obviously is always true but more of an issue due to trying to keep ambulance services and hospital beds free).
Really it would be useful to have multiple voting options covering the difference between ordering from small businesses and Amazon, or takeaways and board games or whatever, but as it is:
YABU - it is unethical to order non essentials online atm
YANBU - it is perfectly acceptable to order non essentials online atm