In my experience, economists don't usually conflate subsidies with negative externalities any more than the conflate positive externalities with taxation.

"Most people don't know the word "externality," so using a less precise term that they do know is not in any way deceptive."

People do know the word 'subsidy' and most know that it means a direct gift or tax benefit by the government which is not the same thing as an externality. What's more, they do know the word 'cost' as well, which is much clearer in this case than 'subsidy'.