This is descriptive vs prescriptive linguistics. It's up for debate whether or not using emojis as hieroglyphs is a problem.

> The problem is that some use them as hieroglyphs.

Well, that's those people's problem. They won't be able to communicate with anybody outside of their group, so they must eventually give the style away or learn to tone it down when talking to strangers.

Not differently from any other kind of group idiom people created at any time in history.

Why is that a problem? I quite enjoy conversations that spell out words using emoji. I admit it may take me a few milliseconds longer to make sense of a hieroglyphic emoji then a spelled out word, but there is some satisfaction involved and I hear a different—more joyful—tone in the sentence.