Thanks for the joke :)
I believe that they are keeping the data in order to make machines smarter.
hum... yes of-coooooouuuuurrrrrsssssseeeee :)
And I also believe they would not use the data against us. I even think it could be illegal, couldnt it?
You are talking about Internet Giants, so you know, laws made by mortals are loosely impacting them :)
Joke apart, they will do whatever they want with the data collected. When you store giant amount of data, this is not just for fun. With data collected , they can extract plenty of information, to feed their AI,... yes, for example to target again more people's interest, and needs. Within the exchanges with Alexa (or other assistants of this kind), they get lot of information about you, your household, your needs, etc... These information can be used to propose again more targeted advertising, but I am sure there a plenty of other applications, that I can't even think about , but sure they did :).
Remember, Amazon is experimenting delivering products to your door before even you ordered them, or even considered ordering them (with the right to return them if you don't want), so by studying your exchanges with Alexa, they can certainly refine again more your interests and temptations.
Amazon can also start selling information to enable other companies to do all kind of profiling , for all kind of reasons, you never know, what can happen.
There is also the problem of hackers, what if hackers are putting their hand on all theses records ? ... you know, hackers can be very creative :) (and I am sure that one day, we'll hear about personal assistant devices hacked, and used to record people stealthy).
Now about how these information can be used against you, I loosely remember a crime story, where the police requested Amazon to give them the recordings from Alexa, I don't remember well, someone will have a link certainly.