Heard this a couple of times from family members recently. I am currently single (31) with 1DC.
Context: DM often buys things for my Gdad and often he'll say it's the wrong thing, even if he asked for something like it in the first place. Sometimes he will even give it back to her saying it's wrong, never mind the fact that it's weeks after she gave it to him and she can't return it. Sometimes food/household items, sometimes more expensive things like appliances. DM gets upset.
We were out shopping recently and she was going to buy something and I reminded her of how it was always the wrong thing and told her not to do it, she did agree with me on this occasion. She tells stepdad when we get back, oh ha ha Sean's so strict blah blah.
Other example. My cousin lives with her DH in London and recently her BIL moved in as can't afford to rent his own flat atm as just moved for job. All fine. Except it turns out he's paying really low rent and DC is doing his washing and making pretty much all his meals. They all work full time. When she complained about this I was like, why are you doing his washing?! And she was like 
Again when we chatting about it with family and I was like why she is doing all that extra work, they were all like "ooh Sean, I feel sorry for your future husband".
Why is trying to not make people behave like mugs make me into this hardline person? Or do I come across as overbearing? Feeling a bit frustrated tbh.