There are two things going on in Servo that are causing it to use a lot of unsafe { ... } blocks. First, it still depends on a large amount of large c libraries

There are two things going on in Servo that are causing it to use a lot of unsafe { ... } blocks. First, it still depends on a large amount of large c libraries, like SpiderMonkey for JavaScript. We automatically treat c foreign functions as unsafe as we can't protect against them doing unsafe things. Second, the DOM is very much built on an object oriented class hierarchy, and we in rust have put off figuring out how we can support that until after 1.0. So Servo uses unsafe code to hack around our temporary lack of support for that feature. So while there may be a lot of unsafe blocks, it should only be for the short/medium term.