Even if the far-left anarchist is merely protesting peacefully?
They did not have a permit, they ILLEGALLY gathered and tried to block a march. They did not march alone or in another area - no, they instead attempted to block the 60k marching. If they were in a different area, had the proper permits, did not antagonize anyone, I'm sure they wouldn't have been arrested. However, they gathered illegally and tried to form a human chain to prevent the NOP guys and the other 60k from marching down the route that was planned wall ahead of time.
Or are you relying on some vague "danger to Poland" to justify excluding people from the protections offered by the Constitution?
That's not for me to decide - that's for the police, government, MIA, MFA, etc.
Also, you can only lose your citizenship if you lied on your application, belong to subversive groups and are charged with treason/espionage/etc, which is kind of tricky because a person would probably serve a sentence if convicted but strictly speaking the PL constitution and government state that generally only a person can renounce their citizenship.
So if the majority of Polish citizens decide that, for example, those who obtained a foreign citizenship should be immediately stripped of Polish citizenship and their property taken away from them, would you support it?
Yes, that's how a democracy and a majority vote works. If such a referendum were held and the majority of Poles wanted that it's their decision - not foreigner residents or outsiders. Being a Polish citizen gives you voting rights to decide certain matters. If a person wants to have a say in such things they should get Polish citizenship. And even once they do and participate in our voting system, they must still respect the wishes for the majority of voters.
I was against the abortion and a few other things PiS tried to push through - however they at least listened to their countrymen and corrected course, dropped the abortion changes, and made concessions on the court changes (although it looks like just a few days ago they pushed some more changes).
In the same way, PO was in power and Poles were furious when they kowtowed to the EU's migrant quotas. PiS ran against that and campaigned on it hard. That's one of the many reasons why they swept clean in the elections. I liked a lot of things PO did, but not everything like how they viewed Polish citizens' wages, their kowtow to the EU, and generally being out of touch elitist EU ass kissers who got a taste of a few millions and then forgot about where they come from and their countrymen.