It's not really the current thru the switch while simply operating that's an issue, it's the turning off of the switch under load, which draws an arc across it's contacts inside, burning them. Same thing happens to a lesser degree when turning it on. At some point, it's not uncommon for the switch to weld shut. Depending on the kind of switch (toggle vs paddle vs pushbutton vs rocker), and what it's made of (metal vs plastic), it might survive being forced off again once. but usualy there isnt' enough torque against the contacts to force them apart before the part you hold breaks off, so your'e stuck with the motor on full-force until you unplug power.
That's why I suggest a plug you can undo one-handed very easily, so you can stop the motor if it gets stuck on like that while riding.
If your brakes are good enough you can still easily stop the bike itself even with the motor on full, but that won't help the motor as it may burn up from the high current at stall before you can get off the bike, let go of the brake, and fiddle with the switch or wiring or pull the battery off.
CrazyBike2 has a circuit breaker right where I can pull it easy, between my knees, because back when I had SLA and a brushed motor on there, I wanted some way to cut off power should the worst happen (never did, thankfully).
This is not an issue with brushless motors, but brushed, controller or not, it can be.
