Do they have pitot heat?
What do you think?
Are the Static ports heated?
Not normally a problem where they are.
Are they aware of the weight of ice that might accumulate?
If you load your plane like the average Warrior with 4 people crossing the Channel on a sunny Sunday on the way to LeTouquet, that might well be a problem
Are they aware of how suddenly and how quickly ice can accumulate?
In stratus cloud, not all that "suddenly"
Have they seen the damage chunks of ice do when they disembark?
Disembark from where?
Are they sure that control surfaces won't freeze up?
They would if you do nothing about it
Can you accurately measure how much ice you have accumulated?
You could climb out with a tape measure, I suppose.
Are you sure the carb heat is still doing its job?
Now, that one gives the game away. I hate to be impolite but you should get back to FS2004
Carb icing is not the same thing as structural icing. Carb icing is caused by the temperature drop in the carb venturi. Structural icing is caused by flying through air containing supercooled water droplets.