Drunken yobs ? Yes and from the pub too.
Unruly children ? Well a pub should be able to decide if it is for adults or families but unruly, yes ask the family to control their kids or go elsewhere.
I feel uncomfortable imposing the restriction as it affects personal freedom, but in fairness it would be good for society if this practice made folk pariahs for future generations. Maybe it is a case of the ends justifying the means.
For sure, at present, the garden is a not a particularly pleasant place to go in the warmer weather, as it seems to be near exclusively set up for smokers. Ash trays (often used) on every table, many smoking nearby where you may wish to go. And anyway, outside office building doors it is already banned, is this such a difference ?
Be interesting to see if it gets taken up.