Well it's not like Players can't use BGCs in their favor. Just like turning the lights out while fighting against security forces that don't have thermographic vision, hiding out in a BCG can be a very smart idea if you're on the lam and afraid of being astrally tracked. Or ambushed by vampires or something.
The difficulty with this is two fold. One, PC's generally have no control over bgc, you can turn lights off, you can't turn bgc on without DAM buy-in.
Two, "Oh, this bgc is aspected towards pollution like HMHVV, he's stronger now."
Fair points, but to rebut I'd say:
One: So long as the GM is being consistent, actually the players can exercise some control over putting themselves inside a BGC. No they can't easily create one themselves perhaps, but so long as the yardstick is consistent about what causes BGCs the players can hide/plan an ambush inside a BGC so as to limit the effectiveness of enemy magic. (Popular parks, lovers' lanes, rock concerts, sporting venues, places of worship, etc all "should" have BGCs). EDIT: Actually if the players are more concerned about being astrally tracked after the ambush rather than magical defenses at the ambush, then they could perpetrate some act(s) that would in the course of the ambush generate a BGC that would then cloud the astral afterwards. Dying people do tend to have powerful emotions, afterall. If the runners are of a sufficiently deviant moral character (and the players and venue are all comfortable with the dark side of Shadowrunning) they can do some things to ensure those emotions are powerful enough to leave a BGC to help mask their involvement/egress. Obviously these sorts of things will torque off police and corp security and will ultimately result in public awareness/notoriety, but options are options.
Two: Saying the opposition is aligned to a BGC is pretty shoddy GM-ship, unless there's an excellent reason for that alignment. Segueing with point one, if the players are deliberately picking terrain with BGCs as magic neutralizers, they obviously won't be choosing the mountains when fighting a Mountain Shaman, inside a Church to hide from a Sylvestrine Mage, and etc)
