One of the key things about being a Tory, IMO, is that when you set/support rules, you always assume there will be exceptions.
The drugs thing is just one example; the principle is vital to their worldview. Not just laws but rules set by orgs like employers, schools, councils.

The thing where you assume there'll always be "reasonable" exceptions makes it easier to accept draconian rules.

"Yes, there will be a prison sentence, but we *obviously* don't mean if it's your first offence!"

It also - this is the main thing - reinforces power imbalances.

When a rule is extremely harsh on the surface but there's unspoken, unwritten provision for leniency and exceptions, who gets the benefit of that leniency? People who already have resources like education, knowledge of the system, confidence, pushy parents, a good lawyer, etc.

When rules are not intended to be always taken at face value, people who already lack power and resources are disproportionately punished.

People lacking money, confidence, charm, negotiating skills, friends in the right places. Stuff like a printer, smart shoes, a shower.

When we assume that rules are to be applied literally and consistently, we take a step towards fairness.

If a rule seems too harsh when taken at face value and applied in every situation, it's probably too harsh.

The penny dropped for me when I met a Tory who'd voted for Boris as London Mayor. Someone asked her if she really agreed with his plans to ban drinking on the Tube.

"Oh, Boris won't stop ME drinking on the Tube." In her head, she was already an exception.

I lived for years in Tory-run West Oxon, and the "rules but not really" thing was most obvious with driving and parking offences. But it applied everywhere, from the rules at music festivals to who could give out leaflets in the town centre and who couldn't.

Even after a child in my town was killed by a pavement driver, people continued to tolerate pavement driving. How? By calling it "parking up", "getting out of the way", "cutting a corner".

They didn't approve of pavement driving, but those doing it were all somehow exceptions.

But my disabled friend who tried to use his little scooter in a pedestrianised (outdoor) shopping area? He was banned. Rules are rules.

The Tory mindset is to excuse those with power and condemn those who don't have it.

Inconsistently applied rules are a great tool for that.