Anyone's free to build that product. Of course, not anyone is capable of this - surely Google leverages immense computing power, complex software and its knowledge graph to do this analysis? You'd need to replicate all that in competition.
But seriously, how paranoid can people be? If anyone really wants to get your data, do you really think it's safe on your server or on your local machine?
By the same token a really determined burglar can get into my house - that doesn't mean I should leave the doors unlocked.
No-one is suggesting that Google are going to hack into your machine to get your data, nor that what they want to do is out and out unpleasant, but what it is in in their interest either instead of or as well as yours.
Until we work out that instead of / as well as, I think a healthy questioning of what might be happening is reasonable.
But seriously, how paranoid can people be? If anyone really wants to get your data, do you really think it's safe on your server or on your local machine?