A few points:
1. Motorists will hate on cyclists because they believe with all their hearts that the roads, and the COUNTRY, belong to them that DRIVE. If you DRIVE 15, you're considered an ass, but you're still a fellow driver; if you ride *25*, you're still trespassing on "their" territory.
2. IT DOES NOT MATTER what the filtering laws are in MOST states; the only filtering law that matters for ANY of us is the one in the state(s) where we ride. In my state, filtering is illegal. NOR does it matter about breathing exhaust, or anyone's 'feelings' -- you disobey the law, you are open to official resolution. Do so at your own risk.
3. "breathing exhaust" is virtually the same on the road, no matter where you are; there are no filters in most cars, it seeps in (or blows in when the fan is running) the interior all the time. There is the unresolved debate about a faster-breathing cyclist either: a.)breathing more in by faster respiration; or b.)flushing the lungs out through the faster action of air exchange -- pick a side. (I personally prefer NOT to be enclosed with the fumes.) But sitting behind a car just focuses the STENCH, that's really all.