What? How was that involuntary?!? Okay the "boom effect" helped in the fight, but it really did not look like Johnny didn't have the option to stay, Max asks him to continue to fight after all. And Johnny *says* he doesn't want to turn back, and he has this blissful and serene expression ("I can feel it calling me... finally. It's...it's gonna be amazing, isn't it, Max? It's up to Flash to beat Savitar. There's nothing more we can do. And as for Jesse... tell her I love her, Max. And tell her I'll always be a part of her. Now... more than ever.") and later Flash explicitly states that the field won't hold anybody who isn't ready, who doesn't want to stay, who hasn't made "peace on the mortal plane". There is no way "involuntary" fits into this.

The plot twist that Flash had to give Savitar what he wants actually worked for me, and I can see the speedsters' POV on joining with their power field, and yet -- on some level I find it disturbing that for them suicide at the right time is the perfect and most pleasant way to die, and seemingly the only way they can have the afterlife they crave, and that apparently for some, if they turn away from it, like Max did, they missed their chance and end up longing for having had that faith then the rest of their life. I mean, in a way Max kind of "atones" for his failure to take this drastic step by convincing others that they should embrace it.