Hi dreadz,
What do you mean that you can remove all of the fields in the repeating section? Do you mean that you can remove all instances of the repeating section so that there are no rows in the "table" ?
To prevent this, you can add custom data validation on the repeating section that fires when number of rows = 0. To do this, double-click the repeating section, go to the data validation and rules, and add a data validation that specifies this. Don't forget to add a nice message!
Matt Faus / Microsoft InfoPath MVPQdabra® Software / Streamline data gathering to turn process into knowledge