Make the Recurring interval field automatically set 'recurring' to be 'on'

We are looking at issues with users being able to select the recurring interval - without having ticked the checkbox for recurring.
Would it be better UI if the interval fields that the 'greyed out' if that check box is not selected?

We are also looking at forcing recurring on some forms - I saw Xav had done some work on this but we are wondering if a patch that added a new checkbox in the contribution config for 'is recurring required' would be acceptable