So basically sniping is when a person or group uploads the newest chapters of a manga that has an active group working on it, often deliberately to undercut the other group. It's highly discouraged because it's often done with mass mtl which iirc is against the terms of service (think services like torii or sakura I think it's called?) And doesn't add much to the quality of the site or manga that gets TL'd. Remember we're here because there is no official TL.
Where sniping is generally considered okay is when the current group working on something is either very poor quality or extremely slow uploads. In this case, EnD took over after Heat but struggled to keep a consistent pace for whatever reason. And these things happen, maybe real life gets in the way, maybe you took on more projects than you can handle, maybe you lose motivation, it's all volunteer work. So for whatever reason they couldn't keep up with the workload. BB was doing it himself on the side but, out of respect, uploaded only to his personal facebook group. I was doing the same thing but just uploading to a mega folder. I don't know if they talked about it or whatever, but BB has now basically taken over and EnD is supportive of it. Things like that or if a group just straight disappears is generally where I, and most people, defend it.
In this case it's considered a bit rude to be suddenly jumping in with, I apologize, but very rushed looking work, as most of the community is expecting something else when they see this pop up instead. It's kind of like dangling spoiler in front of people. A better option I think would be to ask the current uploader if you can help in any way, or has been said earlier, try another series that has no group and needs one. If BB disappears for like a month with no word then by all means go for it.
At the end of the day you are of course within your right to put your own work out there but I just want to explain why the community is reacting negatively.
