Nothing wrong with switching teams. You don't get any reset perks by switching just before. If you switch to the winning team, you get fewer perks for your kills given the perk ratio. And I find it hard to see any even potential problem switching over to the losing team.
As for spies, even the 12 hour switch delay is a pain in the bellybutton for spying with. The people who care enough to spy already, care enough to pay for second accounts for that purpose.
If playing for a certain country ceases to be fun for any reason (only a few vulched fields left, no radar, annoying teammates, whatever) there is nothing wrong with switching teams.