Hi @freemo, how are you? Kids already do write with their both hands. That's how keyboards work. :D
Now, being serious, why do you think people should double the efforts to learn to write with their both hands? They already learn many ways to write and to record information: handwriting; keyboard writing; writing using their phones, recording their voices and even video.
My opinion is that their time should be used in a better way, like how to express their thoughts (writing and speaking), how to construct arguments (traditional academic and modern "feeling based" arguments), or just playing around with other kids. :D
I think handwriting is likely less similar hand-to-hand than you think. I'm right-handed and learning to handwrite Persian (a right-to-left language) gave me a lot of appreciation for the difficulty lefties experience in writing English - the tip of your pen tends to be at an angle where it digs into the paper rather than smoothly brushing against it, you drag your hand through the ink you've just written, etc. It seems probable that the muscle movements to guide a pen along a certain path with one hand are going to be quite different from those to guide it along the same path with the other hand, so much so that it's essentially a different skill.
@freemo @khird @jahnke I guess to make it less inflammatory or context dependent the message can be distilled down to "ambidexterity should be encouraged and rewarded (more)". I for one am often inconvenienced by finding myself with one tired/worn and another weak/fumbley hands, not even sure which one to consider "crippled" at that point... if not both.
@khird
Writing is a bit of a unique case. While it doesnt translate hand to hand it also isnt a x2 effort. LEarning a new script with one hand takes a fraction of the time to learn with the other hand if it already is capable of fine motor skills. But the movements are fairly different so there is some relearning.
In the case of handwriting by nature of the fact english is left-to-right writing I tend to recommend learning to use your right hand for that. Only time you'd need to learn the left hand is if you do a right to left script too.
Though its good to learn despite the usefulness due to just training your brain in general.
@jahnke