{Polar Boy} "... it seems we can go around deleting each other's replies. Is that right?"

Not really. Only the four moderators, and owner Rob Kamphausen, can delete posts. (And a lot of us hope they won't!) They also can edit your posts. (Ditto, short of emergencies genuinely disrupting discussion.)

You can edit your own posts. You can't delete your own posts, though it's possible to edit one down to display no text, if you feel you must.