I avoid bed frames. I made it a policy sort of. Nice to find a piece of that stuff later when you want to drill it. I make a living save/salvage a lot of material but not those.
Agreed, bed frames often are made steel of questionable origin, often rerolled railroad rail.
In my area they are often on Craig’s List but a twenty mile drive.
I have used them for things where strength and finish are not a consideration. They weld pretty good with 7014.
If you’re using it for aerospace application, sure, avoid it. But if you need something entry level to hold up things you’re welding? Hoo-rah. Go forth. An entry level person can learn so much about their science and art by the application.....not what is supporting it. Electrode manufacturers have built industry around joining unknown alloys. It’s ok. Really.