So basically you say the cartel will for bigger future profits, now not reap the profits of non-cartel transactions. (that do give transaction fees, transaction without fees I now disregard, as i find it normal nobody wants to work for free...)

So analogy in the ´real´world in the sense that a cartel of shops somewhere lower their prices substancially, running losses, to outdo other shops to bankrupcy, and after that raise prices and earn a lot of money ?

Also I noticed you talk about 2 things: firstly a cartel not forwarding transactions to other miners, secondly a cartel not accepting transactions from non-cartel members.

The first thing I find completely OK, as they are running risks here for double spends I guess (if somebody double spends in other shop, and they find the block earlier), so up to them... The second not accepting transactions from non-cartel members (thinking about transactions that do pay fees, free transactions no need to be taken in blockchain anyway, as nothing is for free), then the cartel is refuting to earn money, and thus running less efficient than other miners / competing "cartels".

Basically another mini cartel (so not the big evil cartel being talked about) could mine its own transactions, and that cartel also accepting paying transactions from non cartel members will make more money, because they take up profitable transactions out of their own customerbase (out of their cartel).

Thats the whole thing, I dont believe too much in cartels.  Because as we see, the miner that would fake being part of the cartel, is gonna win.
(as the cartel is artificially lowering its turnover (not accepting certain offers on which they do make profit, read: not accepting transactions that do pay fees)

The only real cartel is Government itself (cartel by legislation, or by government making it difficult to enter a market due to excessive cost, etc etc), in a free market (without legislation) I just dont see cartels hold on any long....as each individiual member of the cartel is better of not being member of the cartel. (unless they think of in some future day being able to rule 100%...but they wont think that...)

Or do I completely miss the point you want to make?

What I see as a real threat to bitcoin, is not an economical attack but a political attack. (as to say, some group who thinks to profit from hurting bitcoin, simply ordering 1 million asics, and take 90% of the network.) (how difficult is that gonna be if all fees earned by miners are transaction fees....transaction fees not to be huge, to make a ultra secure network that cannot be overtaken with some billions of dollars.) So basically for bitcoin its a race against the clock i guess.