Present-eqdw is mostly rehabilitated in this regard, but past-eqdw was pretty 'nice guy'. And if past-eqdw had read this, he would only be more upset and more confused.
First off, he would read this in an mocking tone. Maybe it wasn't intended that way. Maybe nobody else would read it that way. But knowing that he was in the target audience, he would take this super personally.
Secondly, and this is really the crux of the issue
> So when I tell you that I’m not going to shag you, it’s not because I don’t fancy a shag, it’s because I don’t fancy you.
This is something that past-eqdw fundamentally didn't understand. Something that I feel most writing on the subject of nice guys misses: past-eqdw thought he was doing everything right. Past-eqdw was following the script laid out for him. Past-eqdw was trying to be a good, upright, laudable person by the standards he was raised by. Past-eqdw was implicitly promised by his role models, social peers, church groups, parents, schoolmates, etc., that these things are the good desirable things that you do to be a good, desirable relationship partner. What he wasn't told was that these are mostly aspirational, not descriptive: Everyone says this but when it comes down to it most of attraction is post-hoc-justified monkey brains. Maybe normal people understand this, but past-eqdw, with his overly scrupulous and slightly autistic brain, didn't pick up on this. He just assumed that when people say "I want X and Y and Z", that if he was X and Y and Z, he would be someone people want.
Maybe other people didn't have this experience, but one of the reasons that writing about nice guys like this post are so upsetting to people like past-eqdw, is that past-eqdw was told by virtually everyone around him that "everyone wants a good partner" and so if you are good, you will be wanted. I was raised, both explicitly by my parents and implicitly by the people around me, to honestly and truly believe that people want nice people, and when you're in that mindset, and you find out that not only do most people not want you even though you're nice, but people start writing blog posts mocking you for thinking this, it's not only upsetting, it's confusing. When all you need is someone to say "so, everything everyone told you is wrong", but nobody will tell you that, how else are you supposed to understand the constant mockery of nice guys.
Seriously, if I could go back in time and rescue past-eqdw earlier, one super easy intervention would be "hey fatass, lose some weight". Turns out most of those rejections from the past were pretty much entirely based on looks. It would have been really helpful to know that, instead of trying to figure it out while everyone (friends, family, past dates, future dates) loudly denied it. It took losing 35 lbs to figure this out.
Finally, I think there is a disconnect in understanding when people talk about nice guys acting like they 'deserve' sex. The overwhelming majority opinion from bloggers like OP is "nice guy gets upset when I won't sleep with him. Clearly he is an entitled jackass". I believe the reality, for most nice guys, is more like what is laid out in this blog post, in section 2. As a guy, who is sincerely acting nice, who is working under false assumptions, and who has no way of calibrating these assumptions because socialization and sexuality are complicated and people aren't self aware and can't think clearly about it, this is what it looks like. It looks like a guy, trying his best to be a good and desirable person, constantly failing, while Henry has no problem collecting wives despite beating them all until they divorce. Present-eqdw understands that this is most likely that Henry is just more attractive and more charismatic than he is. Past-eqdw didn't realize this. Past-eqdw just sees an abusive asshole having great success in romantic endeavours, while he himself tries his best, does what everyone says he should, and fails. And then he gets yelled at for being upset and confused at this turn of events.
Summary: The entire nice guy phenomenon is entirely a function of multiple groups of people being confused, ill informed, and shouting past each other. Anything that smells remotely like mockery is making this worse.
Edit: I didn't mention this, because to me it's implied, but it might not come across: Just as past-eqdw had a fundamentally broken understanding of these dynamics, I think most of the women who are upset about / writing about this also have a fundamentally broken understanding of the guys involved. The misunderstandings are not all one sided.