Thanks to all for your feedback.
It is indeed true that modern cockpits are a safer place today with the advent of CRM. Nowadays a lot of emphasis is put on assertiveness during initial CRM courses. At times I fear that we are going too far and so meet the occassioanl too assertive or maybe arrogant F/O.
That's why I came with this dilemma on these forums. Pressing on with my argument during the CRM excercise might have sounded as arrogance whilst resting my argument might be perceived as weak or not being assertive. After all I could have been 'wrong'.