While I appreciate your concern about road safety, it's a bit rich to assume that all road cyclists think they're above the law. I can assure you, not every cyclist is a menace on the road.
As for your SRM device, I'm not surprised you're having issues with cadence readings. Three chainrings and cadences below 80 RPM can be tricky. I'd recommend checking your device's settings and ensuring it's properly calibrated.
Regarding compatibility with your Powertap device, it should work fine with your Garmin Edge 705, but you might need to do some manual data merging.
And let's not forget, cyclists have every right to the road, just like any other vehicle. It's not about special treatment, but rather about sharing the road and following the rules. Maybe some cyclists need a reminder, but don't generalize us all.