I did sign up to be the free QA. Quality is partly subjective and this game looks like it’s going to be a favourite for me, so I’m hoping to have some impact on the development 
I do expect the retail price to be higher than what I paid for the game though, so I’m sorta kinda getting paid indirectly.
Indirectly, you are getting paid with a QA discount. 
If you knew that the game is Early Access (not finished product that is subject to change) why did you buy it in the first place ?
If you don’t want this to happen don’t buy unfinished products.
Sorry mate there is nobody here to blame but yourself. Steam does warn you that the game may or may not change further and this does not exclude any progress in the game that players may have already made.
You kind of did sign up for it.
A woman I dated when I was younger once told me she made 200 euros. I asked her how, she told me she bought a dress on sale 
Now back to the topic 
I think a lot of people are not informing themselves if what they are buying into and then get upset that some expectations aren’t met. The responsibility lies with you as consumer.
She isn’t exactly wrong though. I apply that logic aswell to reason impulse buys aswell! 
I was just about to say, He kind of did sign up to be a tester. It says this right above in a big box before you purchase the game. You literally can’t buy the game without scrolling past the Early Access note on the store page.
Well that’s just patently ridiculous, obviously. Although if she’d said that she sorta kinda made 200 euros indirectly I’d have to support her claim.
“I didn’t buy this game to be free Quality Assurance.”
It’s early access…you literally did
I don’t see a single sentence stating that the file will be deleted.