Maybe Mark will offer one or more reasons?
'Cause you just
know I'm gonna chime in on this one...
To expand a bit on what SMSW and Larry said, your bike has exactly two physical emission control systems other than the catalysts in the exhausts:
One is the passive air (PAIR) injection system, which takes fresh, filtered air from the air box and vents it into the exhaust stream. This forces any hot, unburned fuel to combust on its way out of the engine. The PAIR valves only open when you close the throttle, but because the ST is already has roll-off performance on par with the Ducati 1098, BMW K1200S and Yamaha R1, improving on it would be tough. All of this happens outside the engine so, again, there's nothing to be gained by disabling it. The real reason you don't want to shut that system off is where that gas will go if left to its own devices. The next place hot enough to make it burn is the catalytic converters, the innards of which have a melting point that's lower than you'd think. Keep burning gas in there and it will get hot enough inside to start melting. Melted converter parts mean less air flow, and as Eddie Murphy demonstrated in
Beverly Hills Cop, engines don't like that.
The other is the evaporative emission control system, which is what you have designs on removing. That's another outside-the-engine system that gathers up gasoline fumes that would otherwise have escaped into the air. What SMSW didn't mention is that when the bike thinks it's the right time, that little solenoid at the top of the canister opens up and those vapors get sucked into the intake to be burned by the engine and make things go. It's like getting free gas, and who doesn't want free gas?
Getting rid of hoses and capping off fittings is what you'd have done in 1977 when Detroit couldn't find its butt with two hands and a flashlight and started putting all kinds of poorly-conceived, vacuum-driven stuff on the intake and exhaust systems to keep emissions down. The ST's not a product of the bad old days.
There is one emission control device on your bike that you could disable, but I'm pretty sure you're not going to like how it performs afterward.
--Mark