Pain is also good - just try to go through your day without it, I'd bet within a year you are covered with scars from serious damage you did to yourself without realizing it. Certainly in most medical cases it would be "nicer" to get the desired result without inflicting pain, but that's not always an option, in which case pain is needful to the greater good. In the psychological realm though many (most?) major emotional catharses are accompanied by substantial pain, and from my own experiences that pain itself can be a valuable tool in spotlighting the subtle "problem areas" where a small amount of personal growth can have profound effects on long-term well-being.
Note that I'm also not referring to the pain/pleasure crossover where extremes can be reinterpreted, and I'm not restricting myself to biological experiences either, but stating a broader principle in that we perceive our universe as spectrums - good and evil for example can't exist without each other - try to eliminate evil and you will find you've only moved the goal post. At some point you reach the point where constant pleasure becomes the norm, and a reduction in that pleasure is itself perceived as pain (Note that I'm speaking of perception, not raw sensory stimulus). The only way to eliminate pain is to condense the spectrum so that there is no difference between the maximums, at which point "pleasure" likewise ceases to be a meaningful concept.
I'll tell you more about plants anyway as apparently you're unaware of the state of research (the root-brains are admittedly still a very recent discovery, but not of the new-age b.s. variety). All plants move in response to stimuli, just usually too slowly for us to notice - really *look* at a tree some time, see how it shaped itself to adapt to dominant patterns of wind and sunshine. That didn't "just happen", those were positions it moved into when the relevant parts were still young and flexible, and if you watch a long-term time-lapse video you can watch it happen.. At a more visible speed there are plenty of flowers which only open during certain times of day, ferns which will curl up in response to a touch, and things like Venus flytraps which close faster than the human eye can track. All in response to environmental stimulus. I'm not arguing that they possess a sophisticated consciousness, but they do demonstrate a degree of simple awareness of and personal adaptation to their environment at least analogous to an insect or simple animal, with available evidence suggesting they might possess something perhaps analogous to the collective intelligence of an ant hive - which yes, does in fact appear to demonstrate a certain rudimentary intelligence in excess of any single ant. And (to anticipate your objection) yes, with ants at least it appears to be born of relatively simplistic responses to a sea of chaotic inputs - but the simple rules lead to complicated emergent behavior, and I for one wouldn't want to try to argue the case that human consciousness definitively is not a similar phenomena.
As for being "brothers" - more like distant cousins, but the fact remains that they are based on the same basic DNA and amino acids as we are, and even many of our cellular processes are the same. That strongly implies that we had a common ancestor, and available research suggests that they possess at least rudimentary awareness. That is enough for me to embrace them as distant kin. And yes, I still walk in the grass, pick flowers, eat salads, etc. I simply try to do so with respect and courtesy. Just as I crush pernicious insects in my home, but usher most of the simply annoying/excessively dangerous ones (like crickets and black widows) outside and encourage natural predators (spiders, etc) to take up residence to keep the general insect populations to within acceptable limits in a more respectful manner (the spider does not kill out of simple annoyance, but in order to preserve it's own existence, a far worthier cause of death to my mind). And those unwilling to cohabit with me in a courteous manner are themselves ushered outside and only crushed if they are excessively persistent in returning.