With regards to the morality aspect, I’ve made a post titled “Mask of Fusion” that would better deal with that. Mask of Fusion [Pitch]
I have an idea with the Kaita and the Nuva Mode, relating to the Mask of Fusion (somewhat). If three Toa fuse into a Kaita (two Toa Nuva and one Toa), the Kaita will be an Inika Kaita due to the three Toa not lining up within the Nuva. This could potentially kill the Kaita and all three Toa within it.
Kinda like that, but instead of the Toa simply glowing all over, it would work in the way I described above.
In the case of the Inika, it’s actually an overwhelming of emotion (depending on the circumstance) and greater internal struggle that empowers the Toa. Because of the damaging effects of the Inika, it is frowned upon. @Idhren @Toa_Vladin @LTVmocs: Here’s a perfect scene to sum up the mindset of the Inika.
Essentially, achieving Nuva is mainly about becoming a stronger Toa than your strongest predecessor, either through raw emotion or hard work. Tahu would probably retain the Inika Mode the longest, assuming he ever obtains the Nuva through hard work at all. Onua and Kopaka are the most likely candidates to obtain the Nuva through hard work, before the others (Gali being a very close second, but she might develop a new way of obtaining it).