I absolutely disagree with this.
If you are able to have savings after all living necessities, you can be using not more than 1% of your income on gambling. No need to think about the budgeting like it is something special.
I spend more on things that add up to me than things that do not add up.
I think at the end of the day gambling can be considered entertainment for some people.
And if you end up budgeting for it, and enjoy it, then I don't really see a problem.
Of course, if it is a massive amount, then it would be better off being invested in something, but life is short and you also need to have some fun...
Some people enjoy the act of gambling, so they can do it in moderation, kinda like social alcohol consumption... As long as there's no massive financial holes, then it should be alright and a budget helps to keep it like that.