The problem is the obscenity exception is also used for things like preventing someone from walking around a public park with a giant sign covered in gore porn. Something like that I think is obviously pretty okay to ban, but clearly it gets misused for a lot of homophobic/transphobic type stuff.
Lion batteries have flames without explosions because of design considerations with the batteries: vent holes that allow pressure and heat to escape a failing battery. It’s possible that if those safeguards were compromised, you could trigger an actual explosion.