As a lifelong cyclist, I'm usually spared the horrors of public transport. Suitcases (and worse) pressing into my coccyx, Metro horoscopes, vomit, delays and the smell of someone else's sweaty armpits – I happily avoid them.

But one new public transport phenomenon has recently crashed into my consciousness. Tumblr accounts dedicated to secretly photographing, uploading and then critiquing fellow commuters, have spored like bed bugs on a bus seat. From the apparently flattering to the supposedly endearing to the allegedly hilarious, there seems to be a blog to capture every kind of commuter.

British law on photographing people in public places is still quite malleable. While the European convention on human rights codifies everyone's right to private and family life, you do not, legally, have to get permission from those you photograph in the street, on the train or sitting on a bus. Meanwhile, despite a European court of human rights declaration that the stop-and-search powers granted under section 44 of the 2000 Terrorism Act were being wrongfully used to target photographers, the law is still apparently misunderstood even by the police themselves.

Frankly, the whole legal issue is murkier than a dimly lit pub toilet selfie. But while the legal argument is fraught, the moral debate surely is not.

Every day, blogs like Men Taking Up Too Much Space On The Train post clandestine pictures of commuters, under the snide and self-proclaimed mission of public shaming. Frankly, if I had a loose assemblage of bulky, heat-sensitive genitals hanging between my legs, I would probably sit with my knees hip-width apart too. Most of these men are doing absolutely nothing wrong. And yet their image, including their faces, is being uploaded to the internet and they are being judged by thousands of strangers, all without their knowledge.

Turn that gender picture on its head and perhaps you'll see why this is unacceptable. Were a man to secretly photograph me – a young woman – upload that photo to Tumblr and invite comments from other users, I think my sisters would be throwing up their hands in horror. And rightly so – the Japanese iPhone has a shutter sound that cannot be turned off, specifically to guard against snap-happy perverts. And yet, I rarely hear the same language being applied to women who upload submissions to Hot Guys On The Train. Last week I saw a man tweet: "Girl sat opposite on tube tried to take a sneaky photo of me. Her flash went off. She was mortified." Mortified she might have been, but was he not also angry?

There is also, of course, the question of money. If these blogs are sufficiently popular to gain advertising space, then those photos are no longer not-for-profit, amusing, public-realm snaps. They are a commodity. And the people in them, by extension, are no longer just strangers on a train – they are models.

As with all photographs, context and composition are key. While it is one thing to take an unidentifiable snap of a fellow commuter's footwear it is quite another to upload a full portrait of a total stranger accompanied by the comment: "Here is the picture of the homeless guy who threatened to kill me after I took his picture."

Of course, some photos taken on transport are funny. Who among us didn't snicker at Hitler on the bus? But that doesn't make it right. Because that wasn't really Hitler, it was just a man, in Plymouth, who got laughed at by millions, without any hope of recourse.

Call me a ludicrous old libertarian. But I, for one, just don't think we should shoot strangers in public spaces.