First, a precision: EasyPrivacy blocks Piwik. uBlock Origin enables EasyPrivacy by default. If you think it's wrong for Piwik to be blocked, bring the issue to EasyPrivacy maintainers.
Now, why is it "irresponsible" for Piwik to be blocked?
Some of us just do not like to have all our movements scrutinized, even by 1st parties -- I personally consider this a healthy stance, I just do not like to be treated as a product.
Also, what guarantee there is that all the data collected by one 1st party through Piwik is not sold to any number of 3rd parties? There is no guarantee -- thus all tracking deserve to be blocked as much as it can. It's for the same reason I choose to not disclose my phone number or postal code at the cash register when they ask in brick-and-mortar stores.