There was one at Bathurst, not Bayview, and the one at Markham counts as a Malvern murder. This isn't exactly a lot of murders. Check out some homicide maps of American cities to see some really dangerous corridors.
If we divide Scarborough into rough quadrants, the NW/Agincourt has 3 murders this year so far, the NE/Malvern has 6, the SE/West Hill has 6, and the SW/Scarborough has 10. I've always believed that if 'Greater Agincourt' and 'Greater West Hill' (and the areas near the Bluffs, of course) were separated from Scarborough, they'd be middle to upper middle class areas with reasonably high property values and very little crime.
The problems with Scarborough lie in what I believe are high concentration pockets of high density low income subsidized housing, and poor urban planning. Scarborough is the city with the largest percentage of these problem areas. Etobicoke for example has them too, but in much lesser numbers and dispersed geographically though distance. It's also interesting to note how its proximity to the airport and major transportation links has allowed Etobicoke's industrial and manufacturing areas to flourish, whereas they have failed in Scarborough.
Subsidized housing isn't that big a deal in Scarborough - Jane & Finch, Flemingdon Park, etc. are in North York and are worse than anything in Scarborough. The much bigger problem in Scarborough is the generally cheap housing. When you have such a huge swath of cheap housing, you're going to get a greater amount of less than savoury folk living in these houses. "Add" poor transit and limited services/jobs, add demographic profiles that result in more gang activity, etc., all under one common banner called "Scarborough," and you're gonna get a mess.
In Etobicoke, Rexdale is countered by the larger Kingsway area, but the 10% of Scarborough that is nice is overwhelmed by the 90% that is not-so-nice, and this 90% is almost entirely lower middle to middle class housing that is cheap, cheap, cheap.
Your point about industry is very interesting: while the airport surely played a role, much of the industry in Scarborough is in random little zones all over the place, not particularly close to a highway...flourish vs failure may be a bit of an exaggeration.