My question is, what genres do you prefer to read? Please do NOT claim you like everything equally, because that's pretty useless in beta reading. If your preference is science fiction, for instance, I would not send you a sweet romance to beta read.
Of course no one wants to turn down work out of hand, but in my experience, people who are not readers of a genre by choice are not well qualified to act as beta readers in that genre. It's a waste of everybody's time and it's a hard slog for the reader, too. Too much like a real (bad) job.
Ha. I tend to agree with you, to a degree. Personally, I love reading Sci-fi books in my spare time, then fantasy, then literary pieces. Probably in that order. And when I get the scattered SF piece, I'm much better able to slot it into the intricacies of the genre and able to make suggestions based on other work. However, most of the beta reading I get are books that are kinda broken and the author is looking for an experienced eye for help. It's not "Did you like it?" or "What don't you like about it?" it's usually more like "Where the heck am I going wrong?" And they need someone with the vocabulary to help them.
And with that purpose in mind, I feel being a leisure reader of the genre isn't as important. Bad writing is bad writing, and only, say, 10-20% more readable when you're invested in the genre. Stilted or redundant characters, mixed-up POV's, or confusing motivations stand out regardless of enjoyment. A doctor doesn't need to be attracted to the patient to see their spleen and liver and kidneys aren't working properly. I've worked on dozens of romances, dozens of series of urban fantasy pieces. I feel the best work is carried by the characters' relationships, and when it's presented poorly it's pretty obvious.
That being said, there's lots of times when I'll take a sidebar on some comments, knowing I'm not the target demographic. "Here is my opinion,
but..." And if I get a book for a genre that's entirely alien to me, I'm either gonna turn it down or make my concerns to the author clear up front. Because I want to do a good job.
Nonetheless, I agree, for 90% of beta reads, for what's more opinion-based feedback, being well versed in the genre is essential.