For a very informative discussion, both pro and con, you should get a copy of the OU’s book, ASK (forgot what it stands for, volume 2). They have periodic conferences and compile source material.
It is a fascinating topic. The gemrara mentinos kala ilan as a fake dye that some used to sell instead of the real techeiles. The gemara gives a set of steps to differentiate the two by mixing various herbs and materials. If color fades, it is not techeles.
However, one of the big problems is that kala ilan which is indigo, is chemically identical to the indigo produced by the mollusk that is thought by the pro-techeles people to be the chilazon, after the processing they prescribe. So how could two identical dyes test differently?
Second problem is that the gemara says chilazon is a dag (fish), yet mollusks are called shavlul in mishnaic language. (Rav Perr’s kashya.)
Third problem is that this mollusk was commonly used to dye purple with a different process for many years up till recently, so how could such a common and well-known creature have been totally lost from our mesorah.
Fourth problem is that gemara talks about potzea chilazon being chayav on Shabbos. I forget the issue here, but something to do with how long they survive after the extraction process.
Also one final issue that it is supposed to appear once in seventy years, but the current one may not have such a cycle.
One halachic side-issue is whether one is mechuyav to do something which will still leave him in the same safek as when he began (not knowing if he has been mekayem techeles). Here Rav Shechter has a very strong rayah on some analogous case, where we do it anyway, even though we can’t be sure if we are doing it right. Don’t remember.
The whole topic is one of the most interesting I have ever studied at the time, just based on the OU book alone.
The worst thing is for some hotheads to politicize a purely halachic debate as if one’s camp has anything to do with this.
The worst thing is