If you find a single scientist claiming the opposite, she/he is probably a genius in some field, but I grant you that is illiterate on basic biology.
The global scientific consensus is that plants and fungi react --very fast-- and accurately to any changes in the environment and take complex and strategic decisions all the time about what they perceive. There are zillions of examples that prove that.
Lets take for example this tiny fish moving its tail fast toward a light spot in the sea bottom and then deciding if it likes the place or just jump and go away. It this a sentient organism? Most people would say Yes.
Well, this is not a fish, in fact is a young Kelp deciding where to settle.
Do you want to argue semantics or do you want to discuss the actual content?
As for the part of your comment that claims using the word “sentient” is pseudo religious and used to wield power over others… I think you’re reading far, far too much into it. I don’t think anyone is using sentience as a tool to justify punishment over anyone else. In fact, it tends to be the people that deny sentience that end up punishing others, for merely belonging to different species!
TL;DR Let’s not commercialize anyone that can suffer. Historically it hasn’t gone well.