Controllers are there to assist pilots so they can conduct a safe flight.
Part of that is providing separation from other aircraft in the air, part of it is assisting in collision prevention on the ground.
Anything else is advisory and the final decision should be left to the flight deck. By all means point out the fact there is terrain close by, or that you are not happy that the aircraft will meet a safe profile, but don't try and fly it for them. Give them the information and then let them make the decision.
If you have done so and there is a still a smoking hole in the ground afterwards, you've done all you can under duty of care since you can't possibly know that any instruction you might have wanted to pass to the pilot could be complied with safely. Indeed, you may have forced an inexperienced crew to step out of their knowledge and ability level so making it more dangerous.