I have often been to mass and before communion taken my coat off, put my phone down ect and left them alone and in plain sight, nothing has ever been stolen, but that does not mean nothing ever will, being Christian does not mean we are without sin, without weakness or do not suffer temptation, perhaps we suffer more than most, perhaps that is why we go to church, perhaps we are weaker than the average joe, perhaps we do need a"crutch" ,or perhaps we just realise that all people do.
I think that is the key, that all people are weak and prone to temptation, that the christian tempted to theive and the non christian tempted to theive both suffer temptation, both are weak both under there own steam are likely to steal but it is because the christian has faith in Christ that supernatural graces are more likely to be bestowed upon the Christian - Jesus said to saint paul ""My grace is sufficient for you, for my power is made perfect in weakness." Therefore paul said "I will boast all the more gladly about my weaknesses, so that Christ's power may rest on me"
and that is why i would and do leave my belonings in Church and why i would never dream of it in a nightclub, pub, football stadium.
But who is in the wrong when the theif steals, am I free from wrong doing, by leaving my belongings am i not putting before the theif the temptation?