There are no technical issues with two switches at once - they're either hardwired to their respective system or the switch positions of the whole panel are polled and sent out over a data bus.
It is, in my opinion, unprofessional. Much like some crews who seem to pride themselves on running through ECAM as quickly as possible instead of sitting on their hands for a bit, pushing the button and making sure it does what you expected is just common sense. Fuel pump / battery / anti-ice / pack... it doesn't matter. Taking just a second or two to think through what you're about to do instead of relying on instinct is the way forward.
As a very new co-pilot on A320, I was a little too enthusiastic in my first non-normal in the FFS. "GEN 1... OFF THEN ON". Reached up and jabbed the button. A lot of relays and contactors clunking, followed by a silence broken only by the trainer wetting himself with laughter taught me a valuable lesson.