Judging by their decision to scrap Legacy Rust, Garry and Facepunch seem all too willing to hand over their hard work to hackers.
You say this as if legacy means much to any of them, but realistically you're crying over ants eating an apple core.
Legacy is a rough, misplanned* alpha that's served its purpose to the developers (that being a first draft of the game they want to make; this is not at all uncommon in game development) and has been taken out behind the shed and tied to a post where it's waiting for garry to eventually come around with the rifle and a heavy heart. He's in no rush to make legacy unavailable at the moment, however.
Hackers are just going to happen, and that's a natural consequence of putting something online for others to use--some are determined to break it and mess with others, because that's their idea of fun. You'll never stop these people from buying your product, so you can either deal with it, or never release anything and give up. And when a piece of software is abandoned by the development team, it ceases to be updated and the cat-and-mouse game between the hackers and devs is over.
* I want to be very clear here, because it looks like I'm talking shit about garry. I say misplanned in that the development team never expected Rust to explode in popularity and sell two million copies on Steam before it's even out of an alpha state, and consequently legacy wasn't coded from the start to be hacker-resistant, and it was more a working prototype than something that's meant for widespread use. Most artists never intend their rough, messy sketches for public exhibition, and legacy was kind of a rough sketch of garry's vision for Rust, in a sense.
It also takes time to make sure things are resistant to exploits, but when you're just trying out ideas it's much more efficient to not worry about security if you don't have to -- and the devs originally planned to not have to worry about security for about a year after they started handing out keys to Gold members. They figured that Rust would have a long quiet stretch with a small group of testers within Facepunch on garry's test server; everyone would be a FP member or someone who understood they were there to test, and things would be cool, and they'd give everything a rework once they were fairly set on the basic mechanics. At first the Rust forum wasn't even visible; you had to first know that it even existed, and then know what its forum ID was in order to get into it.
They were wrong, after someone told Reddit and it went viral almost instantly. Facepunch was flooded with people who wanted an alpha key for Rust, ramping up to a tidal wave of grabby, loudmouthed newbs with zero interest in the community or following rules. At this time, because the devs had misjudged Rust's popularity and left security to a minimum in favour of efficiency, you could speedhack and fly using Cheat Engine, which is designed for single-player games. Oh, and it was in a browser plugin, not a standalone exe, another aspect of the devs' decisions relating to legacy's expected low profile that didn't happen.
After checking the numbers of players (as of 5:41 EST 1/9/15) there are 13,370 people on legacy, and 3,865 players on new Rust. To me, it seems that legacy is surpassing, and will continue to surpass, the new Rust’s fan base. Moreover, the vast majority of reviewer’s have expressed their dislike of new Rust (albeit it is still under intense development) and their desire to have support for legacy Rust.
How long will it continue to surpass the new version's fanbase? Wanna make bets? Six months? A year? Forever?
Because right now, roughly speaking in terms of graphics glitches, performance hitches, instability from patch to patch, and playability, experimental is now where legacy was in the Unity webplayer plugin era -- it's "playable" but has a number of problems that make it unsuitable for long-term satisfying gameplay. And that's to be expected. It's being updated daily; the @RustUpdates twitter feed gets commits seven days a week. This is the reality of game development, especially earlier in the cycle.
Rust is highly unusual in that normally, none of this would ever be offered to the public to play, especially not on Steam. Typically, games take 2-4 years to develop (less if it's on an established engine and especially if it's a sequel, more if it's from scratch/doing innovative things), and traditionally the first two years of a 3-4 year cycle would never be shown to the public, and often not even announced unless leaks get out. Only when things actually hit mid-beta stage would the publisher start sending out screenshots of development builds to gaming publications to start building buzz for the eventual release.
Rust is in a development phase few gamers are familiar with, and expectations are skewed. It takes time, and it's going to get better.
Legacy is more playable than the new branch is, but that will change in time. Of course people want the version they're actually playing to be worked on, but the developers have zero reason to waste a second on trying to fix up legacy when that time would be better spent on finishing a version that's been designed from the start to be more resistant and durable under millions of downloads.
Because that's literally what is being asked. "Hey, stop working on the design you're actually going to finish to come patch up a hole in the abandoned prototype you threw together and didn't expect anyone else to mess with."