Hertford is far from Glasgow. The parade I saw was in Co. Down.
They are sectarian based in that it is a unionist tradition.
Must that breed intolerance?
Why?
"Their very nature is belligerant"
Justify that. It is people walking to a band. That is just your subjective impression.

"they are loud, militaristic and oppresive."
Any band in the street is similarly loud. That is not an argument.
Militaristic? As I observed earlier, not really.
Oppressive? A purely subjective impression.

"In my experience the Lodge marches are threatening to any outsider. That is the feeling I have always come away from them with "
Subjective impression.
You do not like the people who march, so you see them and have all these negative feelings.
It is just people walking with a band.
Show some tolerance.

But I do not live there.