Why not respecting shitty opinions is a duel edge sword

I do agree with this to a certain extent but this mindset is a duel edge sword. First off obviously opinions like "fetishizing a group of people is ok, gay people shouldn’t get married or the whole super-straight thing." are god awful things and I agree that they should not be respected. However this whole not respecting shitty opinions is bad in itself since there is technically no such thing as a shitty opinion. Why? Because opinions are subjective. Let's take the topic of abortion for example. If you are pro-abortion then all the pro-life opinions would be considered to you as a "shitty opinion." If you are pro-life then all the pro-abortion opinions would be considered to you as a "shitty opinion." Lines would literally have to be drawn as to what exactly is considered a shitty opinion which would in turn invalidate and cancel many people's feelings (for better or worse). While also violating our right as human beings our freedom of speech.
Not only that but it would be impossible to do because we as people don't agree on everything. Anything we don't agree with is considered a shitty opinion. On top of that if we don’t respect other people's opinions how are we supposed to have them respect ours.