Bitcoin XT is a client which implements BIP101 (see
https://github.com/bitcoin/bips/blob/master/bip-0101.mediawiki). It will fork the blockchain to allow larger block sizes, and the maximum block size will increase on a fixed schedule, from 8 Mb to 8 Gb over the course of 20 years. Many people are opposed to it, and many also support it. It has caused a split within the community.
The author of Bitcoin XT has previously stated that he would force the fork to occur without consensus. This is problematic because without consensus we would have two blockchains, and because that author has decided to take (near) dictatorial power over Bitcoin. Two blockchains can cause a loss of confidence and thus a drop in brice. There are also a whole host of other issues since they would be operating on the same network.
Now I understand the situation much better.
So it is also related to block size debates
It sounds like a an endless contravention matter, and it is difficult to gather the community upon one view.
Thanks for your explanation