Good morning!
isnt it against the law to take an aircraft, which has no anti/de-icing, into known icing conditions?
Of course it is. In addition to "the law" the rules stated in the training manual of the flight training organisation have to be respected, which usually are even more conservative than what "the law" requires. For example, ours require twice the legal minima for ILS approaches (400 ft ceiling instead of 200, 1100m RVR instead of 550). And of course, they state: "no icing conditions".
But reality is not only black or white, as we all know. In our part of the world, avoiding icing conditions at all cost would mean to suspend flight training between Ocotber and April. So the final decision about wether to fly or not to fly will always be based upon the judgement and the experience (and to some extent the courage...) of the instructor. I have learned my lesson many years ago when our Seminole became nearly uncontrollable within less than two minutes due to (unpredicted!) icing - the only time in 30 years of flying when I had serious doubts if I would make it back home in one piece.
So for me, forecast or observed (or even suspected!) icing below MRVA is a strict no-go criterium. But sometimes it can be a bit embarassing to tell the student (who has taken the day off and driven all the way to the airport) "sorry, but we can't fly in these conditions" while some colleagues or competitors go flying nonetheless...
Greetings, Max