Why not? – Because coworkers need to talk to each other. What's next, jumping off the daily standup call for a while when a colleague you have a problem with is speaking?

If someone is reducing the S/N of a large channel then it is a culture problem that needs to be solved by the management. I have seen a few Slack dramas like that in companies I worked with (e.g. a person trolling), and it wasn't difficult to solve. Letting team members to arbitrarily block each other seems insane to me from a company standpoint.