There isn’t an ounce of hate for firefighters out there, but creating a new flag out of the American flag seems a little wrong. I could see how someone might conflate the two.

Nothing but admiration & respect for firefighters. I’m honesty, though, any “thin x line” flag illicits an initial feeling of “I defend my own despite any potential wrongdoing” instead of the intended spirit of it. That might just be me, though. That being said - I’ve never conflated thin red & thin blue together much.

I don't think I would assume that, and I'd say the majority of people I know have positive feelings towards firefighters. I would say, though, that you might not want the association with the thin blue line image.

I've also seen the yellow line being used for towing and recovery types. I know the difference but not everyone does, and it's uncomfortably close to the apologetics for the worst of LE. Granted, it'll also make your life easier while dealing with those "bad apples", so... shrug

As I understand it, the idea behind the "thin blue line" flag is that there's a "thin line" of police between society / civilization and chaos (which they presume would exist / rule in the absence of coercive force / threat from armed agents of the state). I'm not really sure what the thin red line is supposed to represent, other than maybe an attempt to associate firefighters with police. So, if the goal is to express a need for mental health support for or love of firefighters, I don't think a "thin red line" flag is conveying that meaning to me. Something more direct might better convey that message, if that's what you intend.