They knew they couldn't (probably didn't want to) damage the painting itself. The Mona Lisa has been behind bullet proof glass since the mid 90s, so it wasnt a secret. So they chose something that was relevant to their cause and they probably (rightly) guessed that soup would make a headline when paint or dye has been done so many times before that it might not.
Yes. As the platform becomes more mainstream, it more accurately reflects society at large. Which is extremely toxic at the moment. 😕 I used to think talking about our differences in forums like this would help, but it seems that no one actually wants to listen to anything but their own echo chambers anymore.