Erm, ‘Anarchist’? Step away from V For Vendetta… Fawkes [and his many conspirators] wanted a monarchy - just a Catholic one.
The execution of Mary, Queen of Scots wouldn’t have been celebrated, because if you haven’t noticed, the monarch the gunpowder-plot was against was Mary’s son, James.
Cromwell’s hanging wasn’t celebrated because he had been dead for years when they dug him up and hung him.
If you want to know why the 5th Nov is still celebrated, look at the tensions present at the time throughout Europe over sectarianism, and then the increasing pressure GB was under over faith. Catholics were the bogeyman for many, many years [read: centuries]. Look up Titus Oates. Look up the Glorious Revolution. Catholics were barred from untold positions and privileges such as ownership and even marriage.
Even in the 21st century, it was only last year that marrying a Catholic would have rid you of your claim to the throne, and Catholics are essentially still disallowed from becoming PM [note Blair converted after leaving office - and a senior politician has publicly stated he’ll never stand for leadership of his party due to his Catholic faith].
Case in point of why celebrations are still held over the thwarting of a Catholic conspiracy to kill the Protestant king and nobility - have a look at the fervour with which protestants in Northern Ireland still celebrate a victory during the Glorious Revolution. They totally dwarf the 5th Nov [wiki/video].
Also, it’s a bloody brilliant excuse for fireworks, isn’t it?