Would the SWP have any objection if a future march of theirs (or in which they were taking part) against austerity, or the Anglo issue, was disrupted by a group protesting about the Comrade Delta shenanigans in Britain. As stated above, there’s a time and place.
I don’t think the presence of political parties necessarily represents a co-option of Pride by the establishment. Parties and other groups have been participating for years (I was there 20 years ago). And Pride itself is a complicated phenomenon, with many different strands running through it, some very close to the establishment and establishment politics, with others more removed from that.
What happened yesterday is a little like protests outside the homes of political representatives. It’s not that there’s a problem with protest itself, it’s just that the form of protest is short-sighted and counter-productive.