If someone wants something of yours, the only way to keep it out of their possession is to either bank on their honesty or laziness, or to guard it.
The problem of visual key copying can be easily solved by either making keys in a shape that doesn't allow to see the ridges easily (something like 'E' with middle bar being the actual key) or by making a "dynamic" key that changes shape after you insert it into the lock.
Or just smarter keys like cars have these days (which have pretty much stopped non flat-bed car theft).
Good password selection thinking should be commonsense by now to people who post here, but it seems like there's still a lot of work to be done educating the general (less geeky) public.