Yeah, I really got to agree with this sentiment.
I've been seeing this trend pop up in a few things lately; a VN I played called Fragments Note had the main characters sister as one of the romance options...and even before thermae branched off to let you choose a romance, it featured the two kissing one another.
I've started reading No Game No Life, since the concept sounds amazing...but it's also made ridiculously clear that the main characters little sister is in love with him. I am rather hesitant to continue that book series on that account.
Heck, I read the Love Hina manga back in my teen years, and at one point the main characters little sister starts pursuing him romantically...though his response is a repeated, firm back and firth between "No," and "God No!"
Those works are always really clear to point out that the characters aren't look relatives, just adopted but I don't think that makes it any better. It still feels very uncomfortable.
(To some stories credit, they DO do interesting things with that trope, just as Game of Thrones uses the Lannicest to tell us something about Jaime and Cersei. In Attack on Titan, Mikasa is -for all intents and purposes- Eren's sister, but the issue of romance is a lot more ambiguous on her side, while Eren seems to wholely reject it. Revolutionary Girl Utena has...way more complicated stuff, but again, it's not presented in a positive way)
So...yeah. Anime, please stop with brother/sister incest, and I can't believe I had to type that sentence.