dude, you keep on contradicting yourself. Where in ibanks does one find "speculators" that trade spreads? You must be talking about Post-Crisis Cheat-Bank 2.0: Change the name of your desk and continue misleading internal risk managers and outside regulators. Or what else is a "Facilitation Desk" doing? They still run prop books though they are not supposed to other than warehouse positions from client trades yet most facil desks engage more in gambling and day trading markets than anything else.
I still disagree with you on the job description of market making desks. They are supposed to maximize turn over, not p&l. That is the top priority set forth for them.
Regarding spreading, sure, trading spreads can add liquidity in spreads, but as I said it rarely if ever adds liquidity to the overall market. With overall market I define outright futures contracts, stocks, bonds, options, futures options. Not spreads. The amount of liquidity that swaps from spreads into the direct contract market is minimal.
Look at oil contracts for example, outright oil futures (and for that matter most commodities) are actually very illiquid compared to index futures, stocks, currencies, bonds,...if the numerous commodity spreads (whether calendars or spreads in commodity byproducts or commodity derivatives) really benefitted the outright market then you would see a lot higher liquidity in front month crude oil futures, agriculturals, precious and base metals, livestock, ...take a simple look at the outstanding contracts...they pale in comparison to anything index, currency, bond, or stock related. I stand by my claim that exchange traded spreads hardly add liquidity to broad markets,....
...which brings me back to the point that spreaders should not be considered when attempting to fix the broken exchange traded market, especially fragmented equity markets. A cancellation fee is by wide agreement the best solution to fix this mess, and if that hurts a few spreaders then I think that is a reasonable price to pay to bring back overall trust and confidence in fair and equitable markets.
P.S.: Please do not take anything I said personal, I am mostly sharing facts and voicing thoughts originating from own experience. Which parts you accept as facts is left to your verifying my claims or believing me. Entirely up to you.