Is becoming/learning how to be ambidextrous bad?

No, absolutely not. I've been right hand dominant ambidextrous since birth. It has helped more times than I can remember in lacrosse and in tae kwon do, as well as everyday tasks like cooking or driving. I'm well known for being able to crack an egg in my left while simultaneously sauteeing with my right.

Those who are ambidextrous have an advantage over those who are not in sports and other activities, but also in brain activity. The psychologist I visited while getting my IQ tested explained that those who are actually have their brain more in tune with the right and left sides. So, by training your right hand, your left half is becoming stronger as well, which leads to an increase in scores because both halves are being well used and maintained. It's like the so called "brain games", but without any actual games. It works the same way. In the end, it's beneficial.

Not bad at all! When you brush your teeth, or eat cereal, for example, with your non-dominant hand, you actually build new neural connections in your brain.

What IS harmful, is to be forced to use your non-dominant hand at the expense of your ability to use your dominant hand.

I've been completely ambidextrous all my life, too, but I'm a bit of an oddball in that my left hand is dominant for some tasks (writing, for example) and my right for others (playikng guitar). I need to work on my right hand because for guitar you need to use both, the right hand is the picking hand and the left hand the fretting hand.