Goku thought of Beerus as the strongest force he ever witnessed. I'm pretty sure Goku is well aware of his power level when merged with Vegeta. Goku fought a Beerus that didn't use a percentage of his power and he still thought of Beerus as an unstoppable force. He even said that he doesn't think there is a way of beating Beerus (and remember, he only felt a small piece of Beerus power). So this includes his fusion as well. Vegeta was able to make Beerus up his game to 10 percent of his power. Yes, Vegeta would stomp his merged self if the situation was the same (Vegeta going berserk).
Could he even go Super Saiyan 3? Or 2 for that matter. If anything, I'm sure Goku knew of Vegito power level, even if he didn't display it during his fight against Buu and he still knew for a fact he couldn't do anything to Beerus. Remember, he told us that merging with Vegeta wouldn't stop Beerus (and again, Goku didn't get the same treatment Vegeta got, the 10% added power).
The boys trained which is the reason they were able to access those transformations. That body for Vegeta and Goku was new to them. We have no evidence they can go 2 or 3.
I think they worded DBS differently with Vegito vs Beerus. Will relook at the episode.
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Last edited by carver9 on Sep 2nd, 2015 at 08:45 PM
They didn't have enough raw power and Vegeta and Goku doesn't either. I just looked at episode 5 again and here is Goku exact words.
"Damn, to become stronger you have no choice but to do a fusion with Vegeta. Still, my chances for winning would be very less".
Let me know if you want me to post screen shots. Anyways, Goku basically admitted a fusion would be nothing to Beerus and he's basing this off of the percentage Beerus displayed during his fight against Goku (remember, Z fighters can no sense God's power level). With that said, Vegito would probably get the same treatment the other Z fighters got (minus Vegeta rage boost of course).
You used the boys merge as confirmation for Vegeta and Goku merge not realizing that the boys had to train to become Super Saiyan 3.