MS may not have any intention of taking over the internet and controlling vast numbers of computers, but repressive governments around the world have no such morals. Those of us fortunate enough to live in notional democracies have no guarantee that our assumed freedoms might not disappear overnight given sufficient provocation.
Edward Snowden has demonstrated that even democratic government organisations do not always play by the rules.
Windows 10 does collect more information about its users than previous Windows software. How that information might be used is worthy of consideration. For the vast majority of users, I suspect it won't matter a jot. Those living under repressive regimes probably already take precautions.
That said, Windows 10 is a great upgrade and vastly superior to Windows 8.