As a minor addendum to other answers, there is another problem with writing in kana only: reading speed.
For someone who has knowledge of the relevant kanji, reading the kanji version isn't just a way around homophones and ambiguity, it is actually faster.
The reading speed difference gets bigger as your reader's level goes up and the more you stick to 'conventional' kanji assignments.
I am not a native speaker, nor anywhere near, but I notice my reading speed drop significantly in 'all kana' situations, probably by a factor of 2-5. That factor has continued to increase with my literacy level, so I imagine a native speaker would suffer quite a serious slow down.
This is consistent with some research that suggests fluent readers dont really read individual characters.. they recognize whole words or even phrases at a time based on visual components that are distinctive combined with contextual predictions. If you use an unconventional spelling, eg all kana or unusual kanji, you change the visual form and the reader is less likely to 'shortcut' recognition, perhaps causing a 'stumble' where they have to read more closely. (Intentionally causing such stumbles is a valid technique, and may partially explain why kana are sometimes used for emphasis)
Your readers will thank you if you make the effort to learn to write to the conventions they are used to.