ESPECIALLY if they claim to love Windows 7, needs to realise that those two operating systems are basically the same thing!
Windows 7 is just Vista with a new taskbar, negligible changes to the Aero theme, a new logon screen, and a new build number and name.
Under the hood, there's little (if any) difference, so it's double standards to like one and hate the other when they're the same thing either way! Dx 
The main reason Vista was "slow" was because when it came out, Microsoft was pushing OEMs to sell it on computers that were not (or were barely) good enough to run Vista Basic, let alone the premium versions! The hardware just wasn't good enough, it was ahead of its time. If Windows 7 were released when Vista was supposed to come out and vice versa, people would be praising Vista and hating 7, but it would be worse because 7's system requirements are higher than Vista's. Vista was released too early for the computers to be capable of running it at an acceptable speed, that's why it flopped.  It's not a flaw of the OS, it's a flaw of the 2006-era hardware that Microsoft forced the other companies to ship with it. Mind you, Vista came out in 2006, so the hardware of that era was mainly older stuff, because it takes time for newer hardware to be adopted, that's why it was hard to install on older PCs, because they just weren't capable of running it at a decent speed.
The whole thing is Microsoft's fault for not selling XP on the lower-end computers when that's what they would've run best with, but instead forced Vista on them when they couldn't handle it.
On a proper system, Vista runs perfectly. I've never had it crash on me. Not even once, at least not when the OS itself was to blame. The only time it ever crashed was on an old laptop which was aging badly and was having motherboard problems. So, not related to the OS.
If you're tech savvy enough, and you run Vista, you can change the system files and hack them so that the build number is the same as 7's, and then programs that detect your OS and only work on 7, (Such as IE11) WILL work on Vista, and so will the Windows 7 updates, and possibly even the service packs! You just have to know how to get around these things, is all.