Well, plants are not sentient beings if we consider sentient the act of being capable of conceiving a thought of "self". There are other definitions, but I haven't read one that can have plants in it :P
I believe that plants have "feelings" as much as a calculator can have feelings. They hold states depending on the circumstances that surround them (in calcs, numbers input by a user, and in plants, the position of the sun, the condition of the trunk, leaves, etc.) and act upon them. I may be wrong in that. However, plants do not have brains or complex thought, so I would disregard their rights to be as accountable as humans with the capacity of reason would be.
And I would put to death a TRUE violent criminal
Kid slaps his grandma in the mall, and this is considered battery and assault of an elderly person, so let's put them to death :333
It all exits for a reason, like it or not.
Everything happens for a reason. This does not mean that the reason is a good one or one that should be respected when making new decisions. Maybe a trap was set there to kill anyone who passed, but that doesn't mean that we shouldn't take it out to prevent any casualties when we walk by in a big group.
A kid slapping his grandma is not a TRUE crime. It's wrong. Then again, depends why he slapped her.
And yes plants think. They communicate as well.