Filth, abuse, defamation, libel, harassment, racism, hatred, stolen property – how we deal with the dross is the big question of the digital age, and one that we are no closer to answering. The past month alone has thrown up three court cases that highlight the seemingly impossible contradictions of policing the internet.

The first was the sentencing of Liam Stacey to 56 days in jail, as a result of his drunken, racist tweets promted by Fabrice Muamba's collapse. The judge explicitly said the custodial sentence was designed to "reflect public outrage" at his crime. He was not jailed, then, just because he broke the law, but because his tweet stood out and made people cross. The internet is awash with racist opinions of all hues – but when are prosecutions worth pursuing?

Similar forces are at play when internet users infringe owners of copyright. Jonathan Klein, chief executive of Getty Images, recently said he was "comfortable" with users of Pinterest, the new social media wonder-site, posting pictures owned by Getty. Until, that is, Pinterest starts trying to monetise its site. At which point, according to an interview with TechCrunch Klein and Getty get distinctly less comfortable. It's a problem for Pinterest.

Anyway, neither libel nor copyright theft is a new phenomenon. As Adrian Johns makes clear in his book Piracy, the current piecemeal intellectual property laws exist precisely because of a tradition of piracy going back at least to the invention of the printing presses. The laws are reactive, not absolutes. He argues convincingly that intellectual property exists "only insofar as it is recognised, defended and acted upon". If we stop trying to enforce intellectual property, then it no longer exists.

But enforcement is the problem. Few individual transgressions of civil law on the internet are worth the costs of fighting them: lawyers say that any claim less than £25,000 is largely pointless. Attempts to get the middlemen, such as internet service providers, to take legal responsibility have failed.

So other strategies are emerging. In the high court last month, a maker of pornographic films successfully forced O2 to hand over IP addresses of more than 9,000 users who illegally downloaded films made by Ben Dover Productions. The plan was originally to send the users letters demanding £700 to avoid the risk of being taken to court.

This highlights a paradox identified by Jones: the tactics used in the defence of intellectual property can be as distasteful as the copyright theft itself. In this case, the indefensible theft of legally made films has led to the regrettable loss of O2 customers' privacy. After all, the one who pays the bill is not always the one who watched the mucky movie. It's a morally juicy test case. I can disapprove of what Ben Dover does, yet defend his right to do it profitably.

There is a second hearing due that will set another important precedent, around what Lindsay Honey, AKA Ben Dover, can do with these personal details. The judge, Dover's lawyers and Consumer Focus, the official UK consumer body, will argue about what he can say in his letter to the O2 subscribers, and how much he can demand to make the risk of legal action disappear.

For those who decide to defy Dover's letter and accept the threat of legal action, potential bills are high. A new small claims track for copyright cases is in the pipeline, after it was suggested by the Hargreaves report last year, but the jury is out on whether it will help. The National Union of Journalists and the Creators' Rights Alliance are lining up cases to set some principles from the off.

Saskia Walzel, senior policy advocate at Consumer Focus, says that the extent of copyright infringement online can be overstated, as is the notion that a hippyish commitment to an unregulated internet drives behaviour. Research to be published this month by Consumer Focus found that 77% of internet users think that artists should receive a fair share of money paid for films, music and ebooks.

Meanwhile, the last of the legal challenges to the hastily enacted Digital Economy Act failed last month. This means Ofcom must now start trying to make the act, rushed through in the dying days of the last Labour government, actually work. The aim is to speed up the identification of infringers of copyright; and introduce sanctions such as the loss of the right to connect to the internet.

But the act has fudged the issue of people connecting in ways other than domestic IPs, such as libraries and university servers. The sanctions look badly thought-out, too. In cases of sharing child porn images, orders have long been in place forbidding offenders internet access – but these are increasingly being overturned as utterly unworkable. Again, practicalities trump ideals. The legal merry-go-round stops, and we're back where we started – with unenforceable rules and an anarchic web.