InfoPath Dev

I want to stop the user deleting all sections because then he won't see the red asterisks telling him the section's fields are compulsory.

Is this possible without adding my own button and code?

Don't think there is an easy to do this without writing code or cracking open the xsn.  Have you considered creating your own asterisk outside of the control?  You can have a red asterisk in a calculated value control show/hide using rules that figure out whether there is at least one entry in the repeating section.  Maybe that will work out for you.