In response to Henry:

Attempting to apply contract law to pre-existing intellectual property has the same problems as trying to apply normal property law - it is an analogy that doesn't fit.

A contract is supposed to be agreed before either party makes a contribution to ensure that once the contribution is made the other party doesn't renege on their part of the bargain.

If party A signed a contract agreeing that they would pay party B to create a piece of software, then, once the work had been done refused to pay, certainly that would be a breach of contract. In the case of commercial software however party C creates a piece of software first and then goes out looking for people who will retrospectively pay for it to have been created. There is no contractual obligation for anyone to do this since it was not agreed in advance.

And of course if any given person doesn't pay then C is no worse off than they were before and still has every opportunity to find someone else who will, unlike person B, who may be forced to renege on other contractual agreements (such as paying back a bank loan) because person A didn't pay.

In the first case, party A would need to pay even if they decided they no longer wanted the software, yet clearly in the second case it would be ludicrous to suggest that people must pay for software created by C, even if they don't want to use it. The two cases are therefore not analogous. (BTW, C may go bankrupt because they wrongly assumed more people would buy the software than do, but that could happen just as easily if nobody used the software illegally).

When installing a piece of software, a user may read the contract and agree with it. Alternatively they may read the contract and say "I don't agree with that, I think I should be allowed to use the software without paying instead". They don't expect the author to do anything for them in the latter case, so they don't need to sign a contract to proceed (they may need to click a check-box marked "I agree", but it is debatable that that constitutes contractual agreement - I don't believe its ever been tested in court).

The software author is not providing a service to the user in return for the demands they make - the user is expected to hand over money, and/or inconvenience themselves (by not installing multiple copies of the program for example), but the software author offers nothing in return for this. They aren't offering the physical media since the user has either provided that themselves or someone has paid for it already (if they stole it then that is theft according to the standard definition and not relevant here), and they aren't providing any creativity or intellectual effort, since this effort was already expended prior to the user's involvement.

The only thing that the author provides to the end user in return for their money is access to a service. When the user decides to pay for that service, they are aware that the price includes both the cost of distribution and a markup to cover the original development. The user never agreed contractually that that they thought that the product was worth the price quoted, and if they don't feel that it is then they have the (currently illegal) option of getting the product via a different distribution channel that doesn't cost as much. By doing this they are not violating a contractual obligation, at least not a legitimate one.

If on the other hand they do think the product is worth the price, and can afford it, but still don't pay it, then they are acting in a way that they themselves probably recognise as being unethical, and will have to deal with that. Even then I don't consider that it should be illegal since it is really no worse than listening to a busker in the street for half an hour and then not dropping any coins in his hat.