Before you get flamed by these boards too much, let me save you some headache:
IT IS A MATTER OF OPINION.
There is no hard scientific data to back either school of thought, and personally, I don't see any problem with mixing species.
The issue tends to arise, esp with exotics that have LOCALE specifics (ie same species but diff locales ARE diff even though they can be bred together). People like to keep the "pure" locales separate. I'm all for this but I don't see any reason why people can't ALSO create hybrids.
The issue I think most people have with it is that it dilutes the market and at times it will become hard to tell what exactly you are buying. However, I think this argument is utter bullshit tbh; if you are EXPERIENCED in the field then you will buy from a reputable dealer and not have a problem....if you are not experienced then it doesn't matter.
Just my 2 cents; I see nothing wrong with mixing as long as you are open about it if you try to sell your animals. Someone lieing about his mixed animals and selling them as "true" locales is a scammer (or unlikely, but possibly unaware)....but that has NOTHING to do with the mixing of the frogs themselves.
HOWEVER, as others have pointed out on this thread: There are correct and incorrect ways to mix. As has been said in this thread, and quoted by SCOTT RICHARDSON above.....mixing that many frogs in those tank sizes is plain dumb. Not because of the mixing of species but because of the lack of space/environment htey have.
Mixing geckos with frogs as well, not a wise idea....esp taking their sizes into consideration.
AS A GENERAL RULE: IF YOU PLAN ON MIXING MAKE SURE THEY HAVE EXACTLY THE SAME REQUIREMENTS, THE ANIMALS ARE THE SAME SIZE, AND THE ENCLOSURE IS *MORE THAN BIG ENOUGH* FOR THE ANIMALS. IN A MIXED TANK YOU NEED **MUCH MORE SPACE** THAN YOU WOULD IF THE ANIMALS WERE NOT MIXED. and DO NOT MIX UNTIL YOU ARE VERY EXPERIENCED.
You might THINK they are doing fine, but until you are truly experienced you don't have the ABILITY to see when something is wrong. They don't always show problems; in fact they usually HIDE problems.
EDIT: As a side note, I would like to point out that genetic mixing is the preference in nature. The more varied the genetic pool, the better the resulting animals tend to be. I do not understand the desire to "keep nature pure" by many keepers....nature itself is always evolving. If you were to look at these same animals in 1000 years odds are that these locales would have crossbred and possibly even created new locales....you guys are ok with the "naturally created" locales, but not the "purposely bred" locales....it just does not make sense to me. I am a keeper / forum member of several different exotics and although this attitude changes from animal to animal, there is NO SCIENTIFIC BASIS whatsoever. It is purely opinion. Until SOLID EVIDENCE can be shown one way or another, I will continue siding with the "pro-mixers."