As to your first point, the countries to whose citizens the ETA will apply (e.g. the U.S., Australia, Canada, Japan) are the last people on the planet who would be showing up at the immigration desks at Heathrow or Gatwick and claiming asylum. Check the numbers with the UK Border Agency----how many Japanese passport holders claimed political asylum in the UK in the last year? Last ten years? Ever?

The ETA requirement is not using a hammer to hit a fly----it's using a hammer to hit a fly that doesn't even exist.

Regarding your second point, as I have stated multiple times, what the U.S., Canada (and Australia) do in terms of ETA is immaterial when considering the UK's imposition of ETA. Geography means that the U.S., Canada and certainly Australia do not face the same competition for transit passengers that UK airports do. Airports like IST, DXB, DOH (as well as Continental European airports) are rivals for the transit business of UK facilities like Heathrow. They pose no threat to U.S., Canadian or Australian airports in terms of attracting transit passengers away. Dubai (for example) is geographically completely illogical and inconvenient for people whose itineraries are currently taking them through the U.S., for example. But Dubai makes a lot of sense for many of the travelers who might otherwise connect through Heathrow (e.g. North America-India).