The Toronto Transit Commission has decided that "censored" is the eight-letter word it's most comfortable with.

As criticism mounts, the transit provider says that a $500,000 artwork it approved and paid for – one which allows the public to type short messages for display in a new station – cannot be made operational because of fear of hate speech and profanity.

It's a decision that raises questions about free speech and public space and whether the best way to handle offensive rhetoric is to block it or to challenge it.

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"The TTC has an obligation and responsibility to provide a safe and welcoming environment for all," spokesman Brad Ross argued. "The installation has not yet been turned on and won't be until a solution is found."

However, an artist who has produced interactive works in numerous cities said the likelihood of misuse is tiny and easily countered by other members of the public. A consultant involved throughout the artistic process said that the TTC has long been fully aware of the work it was commissioning. And the station architect said he was "surprised" by the decision.

Will Alsop, who designed the Pioneer Village station into which the art was incorporated, said the installation was a way to "animate your wait" and "an important part of the experience of using the station."

For now, the installation dubbed LightSpell, which stretches nearly the whole length of a station on the new subway extension to Vaughan, remains dark. Terminals on the platform at which passers-by can input their thoughts – to a maximum of eight characters – are working. But the words people type aren't transmitted to the lights above.

"It's censorship," said Berlin artist Jan Edler, co-founder of realities:united, the studio behind the artwork. "I mean, how else would you call it?"

He noted that TTC staff had been aware of the idea since 2009 and that there had been multiple meetings, including with transit agency lawyers, to discuss the possibility of misuse.

According to the TTC's Mr. Ross, senior management have recently been consumed with finishing the subway extension and only very late in the process was "the risk of the art piece … raised."

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Mr. Edler said he heard of the agency's new concerns two days before the official launch of the extension. As he understands it, TTC staff used the installation terminals to input inappropriate words, took pictures of the resulting light display and sent them to then-CEO Andy Byford, whose last day was on Friday.

The artist said he talked to Mr. Byford last week, but they were unable to find a mutually agreeable solution. On Friday, he publicized the issue with a news release calling the TTC's approach at odds with "our work's core objective, which is to strike a balance between new digital possibilities of personal expression and the mechanisms of social control in public space."

In a subsequent phone interview, the artist said he rejected as "ridiculous" what he described as the TTC's idea of having a "whitelist" of agency-approved messages for the installation. And he argued that filtering to block specific words would be too easy to circumvent and would be contrary to the philosophy of the piece.

"It's a very bad sign if we think that censorship and oppressing opinion in public space is the only answer we have," Mr. Edler said. He is hoping for another solution, perhaps by modifying the public's ability to overwrite and delete other people's messages.

That ability of the public to monitor each other is at the heart of the piece, and it's why some observers are sanguine about the possibility of people posting offensive messages.

Montreal-based artist Rafael Lozano-Hemmer said he has done dozens of interactive art pieces and argues that a subtle public pressure keeps the messages clean. People don't post anonymously but instead are physically present and exposed to the reaction of passers-by, making them subject to social codes about how to act.

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"These mechanisms, while they're informal, are intensely powerful," said the artist. He expects that "99.9 per cent" of what people might write at Pioneer Village station would be inoffensive and was scornful of the decision to block the installation, which he said is "making Toronto seem like the backwater of art."