I'm actually surprised it took this long for someone to do this, and even more surprised that serious vandalism only started in 2014 (and that was just paint, this escalated to explosives real fast), I assumed that thing would have been on conspiracy nuts target list for a while.
As long as no one was hurt, I can't say I really care that monument to future genocide was bombed. The only thing I'll lament is the impossibility of figuring out just who is responsible for it. I also don't doubt that it will be rebuilt.
I actually disagree with all of this.
1. It's bad to go around blowing stuff up and destroying stuff, no matter how much you disagree with it.
2. I don't think this was intended as a "monument to future genocide", given it was set up during the cold war, I find it far more likely that they designers felt that nuclear war was likely to reduce the human population to well below half a million without their involvement or action, and this was supposed to be a set of principles for the survivors to follow.
3. It's very likely they'll find the parties responsible. The site is under CCTV surveillance and they got the bombers car on camera, and explosive sales are heavily monitored (and even less regulated stuff like tannerite leaves a paper trail). It will not be hard to connect the dots on this.
4. It's not lively to be rebuilt. The orginal was built 40 years ago on the dime of what's probably one individual kook, or at most a small group of them, and they're almost certainly dead by now. It's unlikely anyone else cares to rebuild it to keep their vision alive.
if the money does get raised, I'll bet it's less "we, the shadowy New World Order propaganda council, will pay to have our guidestones rebuilt" and more "idiots on reddit crowdfunding a replacement to dunk on the guys that blew it up". The only motive to rebuild the guidestones would be petty spite.
And finally, even if the money is available, someone has to actually do it job, and I don't think anyone will do that. Not many people re willing to risk getting bombed to fulfill the will of some nutcase from 1979 and/or a bunch of cringe redditors.