How can I add more people to a group text?

Start here:--> Send a group message on your iPhone, iPad, or iPod touch – Apple Support

Regards

Giulio

There are very rare cases where I feel a visceral hatred of my phone but the fact that we can't, AT THE VERY LEAST, add people to a group text list including non-apple users is F&$^ing stupid. This is the only issue I've run into in iOS that makes me want to smash my phone with a hammer.