Plant sentient-ists are the anti-vaxxers of philosophy

There are two main differences between the two:

1. People who really* argue that plants might be sentient have little to no influence. They are a waste of space, time, and intellectual energy, so that is bad. They make the world a worse place in the same way insect-firsters do, as explained by Dr. Michael Greger here.

Anti-vaxxers are literally killing people and undermining our ability to have a functioning society.

2. Anti-vaxxers can point to medical doctors, people who were vaccinated and died, and people who had bad reactions that might be correlated to vaccines. Plant sentientists point to the writings of a kid whose purpose in life is to get people to tell him he's smart.  

If you've read this far and are interested in more, this report by the Open Philanthropy Project is easily the best good-faith effort to explore the topic of consciousness and ethics. I don't agree with everything, but it is truly an honest effort.

In short, some people confuse the ability to sense (i.e., respond to stimuli) with the ability to have conscious, subjective, morally-relevant experiences. They are not the same thing. But many of these people have lots of time on their hands and a willingness to bury you in words.

One of these things is not like the other.

*Yes, most people who bring up "but you kill plants" are not doing so in good faith.