It is concern about the fact that for much of the history of the hobby, people who don’t conform to a very narrow interpretation of history have been made to feel unwelcome in the hobby as evidenced by the fact that up until about five years or so ago, there were virtually no women in the hobby as well as very nearly no inclusion of anything that wasn’t 100% geared for white males.
Playing for 35 plus years and this has not been my experience. The evidence doesn't support it being unwelcoming either.
RPGs came from wargames surveys back in the 70's showed wargames had as little as 0.5% female gamers at that time. In '79 it was estimated somewhere between 5% and 10% of D&D players were female, while admitted still heavily male dominated, considering where it was coming from if it was unwelcoming you wouldn't have expected a 10 to 20 fold increase.
The first dedicated RPG publication (June 75) was Alarums and Excursions and was published by a woman, Lee Gold.
Flying Buffalo published the major supplement authored entirely by a woman in '78 a Tunnels and Trolls solo adventure by Lillian "Lee" Russell, the editor of their magazine was also a woman Liz Danforth, but prior to that women had co-authored a number of RPG titles.
TSR did seem to have an issue with women admittedly, Jean Wells reportedly having a rough time working there, and it's design staff were almost entirely male.
In the 80's you have R Talsorian Games, founded by Mike Pondsmith coming out with Cyberpunk, ICE had Heike Kubash as a founding member, and had several female authors of supplements. There were a number of other RPG companies with female founding members.
Lisa Stevens and Nicole Lindroos were founding members of White Wolf in the 90s and I think most people see V:tM and the LARP The Masquerade being responsible for bringing a much more diverse group of people into the hobby, that was 30 years ago not five. By 2000 11 of its 28 designers were women. Lisa Stevens went on to be the first full-time employee at WotC (1991), and in 2002 launched Paizo Publishing as it's CEO, Paizo has certainly been well ahead of WotC for inclusivity again still 20 years ago not five.
Admittedly in 1999 WotC survey had women accounting for 19% of players still a two to four fold increase, in about 20 years. However other surveys outside D&D at that time had representation as high as 34%.
I mean there is no doubt that it has been a white male dominated hobby (more so in D&D than the hobby as a whole), but I don't think as a hobby it has been unwelcoming (individuals have certainly been), my experience at University in the 90's rough 33% of the RPG games club was female if not more. At conventions I've been going to since the 90's I met a much more a diverse group of people from different races, sexualities, and gender identities, etc. than I come cross in my everyday life, and online through the hobby this is even more evident.
Sure a lot of the TSR stuff was geared towards white males, but you get a lot more diverse content from 3rd Edition onwards when WotC took control, that was twenty years ago, not five.