Turn off the steam and turn down the iron.
It really doesn't have to be THAT HOT when working with a seam.
I use an iron on medium low no steam (but with the ability to steam if I need it) - my hands aren't warm enough to finger press anything open :)
I'll Starch and Press with a hot iron when the block is put together and before I square it up for the last time. Works well for me.
REMEMBER you're PRESSING (up/down) not IRONING (left/right) the seam.
IMHO I would have to rub hard when finger pressing or using another object to press the seam. People should use what works best for them.