The word 'mugger' is strongly associated with violence.

"The level of guilt which comes with occasioning grievous bodily harm is beyond what opportunists' conscience would allow. "

This is the best, but I would make a slight change:

"The level of guilt which comes from occasioning grievous bodily harm goes beyond what opportunist thieves' conscience would allow."

or, perhaps:

"The level of guilt which goes with occasioning grievous bodily harm goes beyond what opportunist thieves' conscience would allow."

There are many kinds of opportunist. 

The mention of grievious bodily harm implies criminals of some kind.

Are you studying law?

Peaceblinkfriend

“Thanks for replying Patrick.

How do we refer to people who threaten others into giving up their valubles like mobile phones or wallet with a knife? The sort of people I want to refer to do just that but they don't actually want to stab their victim. Are they called thieves? 

I am not studying law but I am taking Legal Studies at school. 

Thank you again

PBF

”

Crime is categorised by laws, but in real life, one thing fades gradually into another.

This list is a mixture of legal and common use of some terms:

Opportunist theft generally implies no violence. Includes 'stealing by finding' and snatch-theft.

Mugging involves the threat or use of violence.

Actual bodily harm, abh, involves minor injury, even, perhaps, a scratch or bruise.

Grevious bodily harm, gbh, involves serious injury.

It may well be that, after the fact, a court of law would question the conscience of a mugger, and whether harm was seriously intended.  For myself, I would take any threat to my person by someone with a knife as a threat to my life.  I wouldn't stop to think about his or her moral stance or conscience.

Peaceblinkfriend

“Thanks for the follow-up Patrick.

So you would refer to the people who threaten you with a knife for your wallet as 'opportunist' right?

I agree with what you said. I am reading about the differring mentality of criminals.

Did you study law?

Thanks again

PBF

”

I am not a lawyer, but I have studied law.  I started studying the history of English law as part of the history of the English language.  I went on to study natural justice, the laws of evidence and administrative law, all from a love of language and philosophy.

I would say that an 'opportunist' is a person who carries out any action only because they were presented with a set of circumstances that made the action seem easy or tempting.  Imagine a roll of paper money left in a car, or somebody in a secluded place with 'portable wealth' such as a Rolex or a high-value mobile phone.  The person who runs past and snatches the wealth only because of the 'easy pickings' is, I would say, an opportunist thief.

A mugger may, or may not be an opportunist.  I would say that any thief who habitually carries a weapon cannot claim in court to have 'given in to temptation' as an opportunist thief.  The term 'mugger' comes from the idea that a person who shows of their wealth in the street is a 'mug', a foolish person, a person who is 'asking' to be robbed.  The mugger seems to me to have an overdose of selfishness, and the knife-carrying mugger even more so.

Good luck with your studies, but remember: a wise man once said that the harder you work, the luckier you get.