Everybody had a different opinion. Is there an idiom for this?

The phrase that comes to my mind is "the lack of consensus".

According to Merriam-Webster, consensus is:

: a general agreement about something : an idea or opinion that is shared by all the people in a group

Example from nytimes.com:

The scientists, several of whom had publicly debated the hurricane-climate connection in recent months, said they were concerned that the lack of consensus on the climate link could stall actions that could cut vulnerability — no matter what is influencing hurricane trends.

That sounds like you are looking for:

Opinions are like assholes, everyone has one and it stinks.