Mary Fisher wrote:

But is plastic ever benign - coming from non-renewable sources at the
moment?

If it's long lasting and suitable for the application, yes it is.

For example polythene bottles are excellent for certain applications
because of their inertness (can't say inertia can you!). Any sort of
bottle has a raw materials cost, for certain applications plastic is
best even given that it consumes some oil.

--
Chris Green