In fact in my experience which dates back to the 1960s they never have been. The backwaters of our cities always have been the haunt of those 'up to a bit of no good' trying to avoid the attention of the law and have long been the scene of drug taking, graffiti, muggings and the like.
Attract low level crime
The suggestion that BW's attempts to get more people on the towpaths is the cause of this is just not true. In recent years, perhaps as boats have got more expensive and luxurious we have cultivated the impression that the waterways are a safe haven from the outside world, and ignored the reality which is that they also attract low level crime.
In fact if BW is successful in attracting walkers and law abiding visitors their presence will deter the more undesirable elements.
A more level headed view must be to regard cruising as a possibly hazardous activity with it being the responsibility of boat owners to protect themselves as far as possible by using the same common sense they would exercise if travelling in an unfamiliar city, stopping only when they feel it safe to do so.
This does not mean hiding in gated marinas but just choosing to stop near other boats, or in well lit areas or out in the country.