should i remove villagers trades?do they ruin the currency?

i am hosting a Vanilla+ or semi mudded SMP
For about 15 - 30 players
where everyone has his own base and there is shops etc.
(something as hermitcraft)
the point here is that
The currency is diamonds
and i feel that villager trades are op specially when u can trade sugar cane with diamonds (or naything cheap with diamonds)

so

1- do u think that villagers ruin the currency?

2- if they does what should I do?
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