That's a good question and I get shouty myself. I suppose the answer is (for me, I can only talk for me) because some views, if they were more widely adopted, lead to some terrible situations.
I think a lot of people have no idea of the end implications of the views they push, and what they mean for the individuals they affect. There are some people who frankly seem to have lived very cushioned lives and will happily define how other people live, while having no idea of the reality of what they are pushing, and how it will affect people.
(A extreme example are the anti-abortionists whose daughters get preg .... and then it's been known for them, when faced with the reality of an unwanted baby, to drive the daughter to the back door of the abortion clinic and get the foetus aborted Then they turn up the next week at the front with "save the baby" placards. They rely on the clinic's code of privacy. It's happened).
The lack of respect for individuals' choice over their own body and lives is honestly wrong, for me. It's not only in this issue, but others. In other cases the elevation of feelings over logic and proportion, which is a countrywide issue, is infuriating (I'm aware of the irony there!) such as the poster who is anti-abortion because she cries for the aborted foetuses. Absolutely no nuance or wider awareness.
It's a flaw in me that I get shouty and sneery, really.