Attacker may not be forced to attack if attacking player has to pay a cost

[LevelX2]

My opponent enchanted my juggernaut with oppressive rays. this forced me to attack and pay 3 every turn, even though it shouldn't (see gatherer rulings for oppressive rays). this actually caused me to lose the game at one point because i tapped out on my first main and subsequently couldn't proceed past the declare attackers step.

http://www.slightlymagic.net/forum/viewtopic.php?f=70&t=15174&p=160694#p160655