The Rambam (avoda zara 3:6) has an entirely different peshat in worshiping avoda zara out of "love and fear". The Rambam says that it is not an external love or fear, rather it is a love for the avoda zara itself or a fear that the avoda zara may cause you harm. The rambam writes that if the he actually accepts the avoda zara as a G-d, he is gets stoned, but if he he worships it just out of the love of IT or the fear of IT, he is exempt. The kesef mishna explains that the Rambam doesn't agree with rashi's p'shat because then the "fear" would mean fear for life, which is an o'nes and he wouldn't be chayev misah even according to abaye, as the rambam holds in hilchos yesodei ha'torah. Based on this, both the first peshat of Tosafos and the Rambam agree that one who worships out of o'nes doesn't receive capital punishment, just that the rambam considers this to be even according to abaye, whereas Tosafos would limit it to rava.
The difficulty with the Rambam's approach to "love and fear" is pointed out by the kesef mishna in the name of the Rivash, that all avoda zara is worshiped out of love of it or fear of it causing harm. That is classic avoda zara for which one is certainly chayev misah! The Rivash therefore explains the gemara similar to rashi. Regarding the question of the Rambam that even abaye should agree that o'nes is not responsible, the Rivash says that "yir'ah" doesn't mean a threat of death which would reach the level of o'nes, rather just fear of harm.