A laptop on the lap is like playing with broken glass. You might get away with it but it is plain stupid. As with glass, you may not notice the sharp little shards penetrating your skin until later. They are so hard to get out we know its better not to take the chance of them getting in, in the first place. The multiple types of electro-smog that come out of laptop computers impact everything around them, just like broken glass. Far better to use one on a table and then only for a limited time.
If you are, at some point in the future, like the EHS today, reluctantly obliged to accept the consequences of perhaps a reckless or uninformed attitude to the biological effects of virtually constant immersion in EMR, it may be too late.