I was so upset when airlines started their "liquid" restrictions and we couldn't carry toothpaste anymore. On over-night international flights, they do provide a small toothpaste with toothbrush but not on any of the other flights. I'm okay with the rare use of disposable toothbrushes with toothpaste. Especially when it's an emergency situation like a natural disaster.
But I don't think that we should promote the use of disposable toothbrushes on a regular basis because it ends up at a landfill after only one single use! It's not environmentally friendly at all unless people always recycle them. And I doubt they do since it's usually used "on-the-run" or while travelling.
We need to promote products which can be used for longer periods of time and which are more environmentally friendly.