so whats the problem?
The problem is this little thing called copyright, which now lasts for the life of the author + 70 years (or 95 years for corporate ownership) -- or about 2 quadrillion years in internet time.
Of course there's a lot of shades of grey in the mix as well: While game play is not copyrightable (meaning you can freely make a 'similar' game) you can NOT just 'borrow' the original title or graphics, or even use 'confusingly similar' names and such.
The whole point about copyright is that it prohibits others from stealing your work. It doesn't matter that you spread something for free without monetary gain -- the whole issue with so-called intellectual property is that it's not yours to spread in the first place.
Now, if you don't charge you're more likely to stay below the radar of the original copyright owners, and if they do decide to sue you then not charging anything might be a mitigating factor in deciding how much money they can squeeze out of you, but that doesn't make it OK.
Now, you can make whatever you want for personal use in the privacy of your own home, but as soon as you start giving it away you'd still be violating copyright laws.