It's not really Mojang's fault. Also, why don't you ask for help in the support section and some person that's really good at technical stuff, unlike me, will help.
You can always play older versions; I still mostly play on 1.6.4 myself because of this (some sort of bizarre hardware/software conflict, the game, 1.7 anyway, runs fine if I can get rid of it but only sometimes and only until the next time I play, at least it doesn't return while playing), with some additional features, including some added in later versions, modded in by myself (another reason is to avoid terrain generation bugs when generating new chunks - I actually modded in new biomes without causing noticeable chunk walls since the underlying terrain generator is the same).
You can play an older version by clicking on "edit profile" in the launcher and under "use version" select the one you want to use; you can even play the earliest versions if you want (alpha/beta, even back to before the game was even called Minecraft). Also, if you play more than one version I strongly recommend making a new profile for each one and changing the game directory (you can just add to or change the ".minecraft" at the end and it will create a new folder for you, it can even be set to a different drive) to avoid loading your worlds in the wrong version, which can corrupt them, especially if you try going back from 1.8. Otherwise, always select a particular version, not just "latest version" so you aren't automatically updated to a possibly laggy/buggy version until you know it runs well; if 1.8.1 fixes the lag in 1.8 you can then just skip 1.8 or whatever version is a problem.
Of course, if you play on a server you pretty much have to use the latest version if the server has updated to it, but I know some haven't updated yet or reverted due to lag problems.
You can play an older version by clicking on "edit profile" in the launcher and under "use version" select the one you want to use; you can even play the earliest versions if you want (alpha/beta, even back to before the game was even called Minecraft). Also, if you play more than one version I strongly recommend making a new profile for each one and changing the game directory (you can just add to or change the ".minecraft" at the end and it will create a new folder for you, it can even be set to a different drive) to avoid loading your worlds in the wrong version, which can corrupt them, especially if you try going back from 1.8. Otherwise, always select a particular version, not just "latest version" so you aren't automatically updated to a possibly laggy/buggy version until you know it runs well; if 1.8.1 fixes the lag in 1.8 you can then just skip 1.8 or whatever version is a problem.
Of course, if you play on a server you pretty much have to use the latest version if the server has updated to it, but I know some haven't updated yet or reverted due to lag problems.
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?