It is likely that when carcinogenesis occurs it is at levels hugely higher than in swimming pools. It is unlikely that in a century old process, with large numbers heavily exposed that cancer could be produced without this becoming obvious. And there are many industrial situations, including hospital operating theatres in which high levels of a haloform viz chloroform has existed for a long time and it cannot be shown that cancer is caused. This is a complex subject. Many processes are involved.
Chlorine has a bad reputation.
Health protection, is quite rightly a priority, however green issues can be overwhelmed by emotion and truth is usually consistent with commonsense. On a statistical basis this would seem extremely unlikely. There is a much higher incidence of and tendency to asthma in children and adolescents, very many of whom are heavily exposed to the swimming pool atmosphere. Not only that but in the swimmers breathing zone the concentration of chloramines is far higher than in the breathing zone of pool professionals, such as teachers and lifeguards. As mentioned, the conventional wisdom is that these competitive swimmers have selected themselves for this sport because of conditions being particularly favourable for them.