I'm not sure that plausible deniability has much value if, say, a user's ISP has a policy of suspending accounts that attract too many complaints about copyrigh

I'm not sure that plausible deniability has much value if, say, a user's ISP has a policy of suspending accounts that attract too many complaints about copyright, hacking, spam, etc. The account itself is a nuisance to them, regardless of whose fault it is.