YABU.
I can't give a full on answer ATM but what it boils down to is the right to do as you please with your own money - and yes, welfare is still their own money.
Where does it end?
No drugs
No alcohol
No treats
No car, walk or get the bus
No new clothes - you shouldn't be buying new things at the expense of the "tax payer" (even if they've paid in for years and years)... etc. slippery slope I reckon.
Also, what does it count, and for how long?
I smoke weed - don't care who knows it. I wouldn't call it a habit as I can go anywhere from 6-20 months without touching it and won't be arsed ATM I've not had any for a year, but if I decided to have a joint tomorrow while out with friends then lost my income and needed to claim welfare, would you support cutting my benefits or removing them?
In addition to this,
A heroin addict won't suddenly go oh I'll lose money oh ok then I'll stop.
Children will go hungry/hungrier.
Women will be forced into prostitution and men will probably rob gas stations. All in the name of saving what, $500 a fortnight?