You know what is GTS?

If not, it is a system of exchanges of Pokémon games

Like, you put a Pokémon as a Caterpie and asks for a Weedle.

If someone else, enter the GTS, have a Weedle, and want to trade with you, she exchange and everyone is happy!

But a lot of people asking Pokémon useless and catchable by mythical, as a Mew. The more applications in the GTS are Genesect and Melloeta, and I honestly do not see the slightest grace these Pokémon. See the following example:

As in this example, the guy is asking for a Weedle BY A MEW! Mew is a Mythical Pokémon, ie is uncatchable in any game. (Except in the Pokémon Red, Blue and Yellow you do Glitch Mew) So it's not at all fair this exchange .These people do not have the slightest notion that anyone will exchange a Mew by a Weedle.

Now let's talk about Genesect and Meloetta

Genesect

Melloeta