Fair-minded citizens who go to see Buying Sex at the Hot Docs festival in Toronto may enter the cinema assuming Canada should abandon its out-dated, puritanical laws and legalize prostitution. They may exit thinking something else all together.

"The message if you talk to any right-thinking liberal person is yes, let's legalize prostitution. Yes, it's the right thing to do," observes filmmaker Kent Nason. "… but do you want to have a 14-year-old girl selling sex on the Internet? Do you want an 18-year-old to decide, 'The only way I am going to pay for my college degree is in a brothel?'"

"If we decriminalize it, it will be college and university students who are targeted," adds his partner, Teresa MacInnes, noting that the clients, many of them married and middle-aged, demand young women.

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In Buying Sex, Nason and MacInnes have waded into the complex debate over legalization just as the Supreme Court of Canada gets set to consider a 2010 Ontario decision that struck down laws against pimping and brothels. Researching the documentary, they discovered two very different groups of women, with diametrically opposed positions. One group, fighting for legalization, is made up of the "sex-trade workers" who insist they have a right to use their own bodies as they please without police harassment or social judgment.

The other represents the "formerly prostituted women" who argue that the practice enslaves women who are poor and, in Canada, predominantly native, often while they are still too young to make informed choices. That group wants to see the johns criminalized instead of the prostitutes.

"The abolitionists want to get to the core issues – poverty, sex abuse and gender equity; the other side says you can't get rid of it so legalize it," MacInnes explains.

In the film, those who wish to legalize prostitution are represented by Toronto lawyer Alan Young and his clients, the whip-snapping dominatrix Terri-Jean Bedford and the eloquent former sex-trade worker Valerie Scott. In the aftermath of the horrific Robert Pickton case, Young successfully argued that the laws against "common bawdy houses" and "living on the avails of prostitution" were unconstitutional because they made his clients' working environment unsafe – by forcing them onto the streets. (The Ontario Court of Appeal upheld that decision last year; the Supreme Court will start hearing the Canadian government's appeal of the decision on June 13.)

In the doc, Bedford and Scott are depicted as media darlings, as they convincingly argue it is silly to legislate against a profession that fulfills a basic human need. But a different group of women has a very different message. They are led by Trisha Baptie, a former prostitute in Vancouver's Downtown Eastside, who covered the Pickton trial for a blog and now advocates against prostitution. In the doc, she pithily states that actually, farming is the world's oldest profession, and travels to Sweden to study how that country has criminalized the buying rather than selling of sex, cracking down on the johns.

MacInnes met Baptie when she was still working in the sex trade and included her in a 1994 documentary about teenage mothers entitled Teen Rebel, Teen Mom. They reconnected in 2007 when MacInnes read some of her writing about Pickton.

"I was extremely happy she was out of prostitution … then I found her writing very interesting. I started thinking about it in ways I hadn't before."

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MacInnes was researching the topic when Bedford vs. Canada went to court, giving the documentary a developing news story to follow.

"When the Bedford case happened we were still in development," said National Film Board of Canada producer Annette Clarke. "It became clear to all of us that what was happening in the legal arena was going to dominate the debate. This was an opportunity to tell the story from the point of view of women in the trade. Hopefully the Canadian public will be able to understand how complex the conversations are."

Buying Sex does not take sides: Nason and MacInnes point out that both groups agree prostitutes need a safer workplace, want to see the decriminalization of the women and are opposed to human trafficking. The film also includes many interviews with johns, regular guys who tell familiar stories of uninterested or unadventurous wives. Still, Buying Sex does leave the clear impression that legalization, which has been tried in New Zealand with mixed success, is a simplistic answer to a complex problem, and that discussing prostitution as a sexual issue rather misses the point.

"It's difficult as a society to deal with the hard issues," Clarke said. "It's easy to say this is about choice; it's harder to say this is about gender, race and class."

Buying Sex premieres at Hot Docs in Toronto on Wednesday. That screening is sold out, but the film will be shown again at 1:30 p.m. Friday and Sunday at the Scotiabank Theatre, and will be available as a paid download after June 6.