You seem to mistakenly think that the Software Updater is some kind of external, or even third party tool that was installed without asking. That's not the case - it's simply a new avast! feature, just like the AutoSandbox, for example; many new features have been introduced throughout the past years.
You installed avast! to prevent viruses infecting your system. Outdated software is the main way how computers get infected - so by making sure that the important software is updated (well, it's not really "making sure" - it's just suggesting, you don't have to install the updates), it protects your machine from infection - i.e. it's doing its job. It's always better to fix the holes into the system (by installing the updates) than trying to detect all the possible ways malware can use to exploit them; sure, we try, but updating is simply more reliable.
The next version will have an additional option to disable the feature - in the meantime, you can simply remove it, as Tech has shown.