> For me, the ultimate laptop bag is one that looks nothing like a laptop bag; it should look like nothing special at all.

Why, exactly? Is the thought that a thief is less likely to steal your laptop if he thinks it's a bag of groceries?

All of the other shortcomings seem to vastly outweigh the gain (lack of bang/bump protection; the fact that you're carrying a laptop in a grocery bag makes it more likely to naturally sway and bang against your leg as you carry it; that if you set it down like a grocery bag it will probably topple over due to lack of structural integrity; that you're leaving it out in the open rather than concealing it in your backpack; etc). And for all that trade-off, I'm not even sure what problem he's trying to solve in the first place that he feels his laptop bag should be inconspicuous above all else.

And it is easy for a thief to see that a bag is heavy and slim to judge that it contains something valuable. Anf then the thief can just forcefully take the bag from you.

In Barcelona there are a lot of cases when a thieve on a motorbike would try to snatch a bag or women handbag from a pedestrian waiting on a red light.

With a back pack it does not work. The drawback of a backpack is that a thief can just open the backpack or even cut with a sharp knife and one would not notice. But more expensive back-packs with a good design have protection against cutting and easy opening while on the back and with a cheaper one can be held in front.