Edit: Copying of media has been prevalent since the 80s
Way earlier than that. My father has a collection of tapes recorded of the radio and other tapes dating back to at least the early '70s. Even back then copying music was common enough for DJs to have started talking over the start and end of tracks to ensure perfect copies weren't possible.
I believe that if you copy a game in a manner that the copyright holder does not approve of, that is wrong. Do you argue that it is right?
I argue that it is absolutist statements like this that are the whole problem. Why should copying games or music be wrong? At least at one time, and I think it may still be the case, it was illegal to even make backup copies to avoid damaging the originals, or to copy music from a CD to the computer you actually use to listen to music. If the copyright holder doesn't approve of that, they can go and **** themselves.
The problem with piracy is not simply "things the copyright holder doesn't approve of", because many of their opinions are simply retarded and not worth listening to. The problem is the actual loss of earnings due to copies being bought and sold, or just distributed at no cost. I have no problem at all with there being laws against that, whether you consider it equivalent to theft or not. It's when people start demanding control over things I do with my own property in the privacy of my own home that the real problems come in, particularly when those demands are incredibly stupid things that have no effect whatsoever on the people doing the demanding.
As a bit of an analogy, take speed limits. Most people would probably agree that 30mph is a reasonable speed limit in a residential area. Some will drive too fast, some will drive to slow, but most people will at least make an effort to obey it. If the limit on the same road is lowered to 20mph, people will be less happy. If it's an uncluttered, good quality road that's had no accidents, they're likely to be rather confused why the limit is lower and you will get less people obeying it, since it doesn't actually affect safety at all. If the limit is now lowered to 10mph, pretty much everyone will ignore it completely. Not only is that an utterly stupid limit to have in most places, with the limits on analogue speedometers most people won't even be able to tell if they're breaking the limit or not.
With stupid laws and crippling DRM, the situation until very recently with media was the 10mph limit. The reasons for having a limit may have been sound, but it was implemented in such a way that it was almost impossible not to break the law in some way, and therefore no-one really cared about breaking it in other ways as well. With the relaxing of DRM by most companies, and generally more convenient ways to get media and more sensible rules covering, things are definitely improving. However, I don't think we're there yet, and people making arguments such as the one you make really don't help matters.
Why wouldn't you download a demo?
Because many games don't offer demos at all? Because many demos aren't really representative of the game? Personally I've never downloaded any games and I mostly rely on reviews and word of mouth. But that doesn't make the "just download a demo" argument any better, when often it's simply not an option at all.