Please expand?
Sweeping statements are just that...sweeping. How is it harmful.....and why do you think this.

And expand I will do. As you say, The Stoop holds 12,500, which iirc is about 8k less than the game Aus vs NZ got last time they played in the capital (2005?). Say the Stoop sells out, thats already a hell of a lot of fans wanting to taste RL again, not been allowed in.
Secondly, I doubt a sell out at the Stoop will get many more people in who haven't already been to Quins. I would guesstimate that quite a siaeable chunk of the crowd will come from not far away or by RL fans travelling from around London or the area around it.
Now if the game was played at a ground like Craven Cottage (just an example, you can substitue it for another similarl capacity ground) then there is potential to not only get that same crowd again but increase it. Say 20k go to the game. I think that quite a few new fans from around the area would go to the game. If Craven Cottage was used then maybe some of the old RL fans may go again.
The Quins RL marketing team could go to the game and market themselves to 20k fans. It could even be more fans than that to market to.
I'm not knowledgable on the geography of London but if there is an increase in interest in other areas of the capital then it can only help Quins.

plus it gives the impression of being "small time", rather tahn being a big event that people should want to go to. Play the games at bigger stadia - and try to create a buzz around the game, rather than admitting we cant fill these bigger venues.

How did Quins RU attract 50k for a standard league game in London - they promoted it and built up interest. Probably most of the people who went were not regular union fans before that game, but I suspect many have been back since. Sadly this would be too much like hard work for the RFL.

Granted - this would have been easier had England put in anywhere near half a performance at the World Cup.

Thats exactly my thoughts. I won't be going to any of the games except maybe the Elland Road game (will have to look at my finances at the time but should be able to go). Since I have been following RL (2002) I have only ever gone to Elland Road and COM to watch international RL outside of Hull as they just don't fill me with excitement as they dont have that big game impact. I wasn't going to go to any of the games last year, I only went to the game in Hull as it was the day before my birthday.

I'd have thought any excuse to get out of Hull for a few hours would've been seized upon?

Thank You...
Alas, of the 12,750 who attend this game, not many will return, as the apathetic nature of the antipodean requires a ground close to shepherds bush to have any chance of turning out on a regular basis. I see your point, in that, there would be an opportunity to get them interested in the stoop for future games, but when your average ozzy looks for twickenham and sees it's not on a tube map....well, let's say he aint going to have it!
So, we have the game at the Stoop and 2 things happen.
1. The BBC ITV and any other station will refer to the game being played at the HOME OF HARLEQUINS RUGBY LEAGUE.....therefore raising our profile and secondly, WE GET TO KEEP THE BAR MONEY!
Oh...thirdly and as happened this weekend. Whilst we had the occassional bitch about how far away TW2 was from town, we did give the majority the chance to find out for themselves. It is a 11 minute journey from Clapham and a 6 minute walk

But are those grounds available? soccer clubs do not want rugby played on their nice pitches in the middle of November and grounds of that size haven't been able to invest in the grass and all the stuff under it that places like Old Trafford have.

Like it or not, soccer clubs in the Premier and Championship don't really need our money any more

I don't care if Eng/Aus is played at the JJB, Belle Vue, Wembley or my local park - if I can afford it and can get there, I will be. The venue really does not matter - it's the fixture which gives it the 'big game impact.'

Saracens have been linked with a move to Fulham, but are staying at Watford for the time being rlhttps://news.bbc.co.uk/sport1/hi/rugby_union/my_club/saracens/7899104.stmrl