This is not an opinion but a fact:
That is incorrect, if it was a hardware problem it could be difficult to diagnose and problems may (or may not) increase in frequency and/or amount in a matter of time.
There are many who have an increased amount of problems or increased frequency caused by hardware, but also many who have problems that aren't frequent and do not increase which are also caused by hardware. For example when starting a program you get a BSOD, this can be caused by a bad sector on the HDD where the program is installed on, with this situation as example nothing else causes a crash except for the single program that is installed on the bad sector.
An upgrade may cause problems, the best way to solve them is by performing a proper clean install.
Thus you would then need to delete all partitions until only 'unallocated space' is left and choose that to install on.
Activation isn't something to worry about, Windows should be activated automatically in the first boot after installation.