If you break the law, you get arrested. I know liberals are trying to undo that across the entire country but it hasn't been undone yet. When liberals get their way and everyone is free to break any law they want, then maybe you can whine about it. But, for now, people breaking laws are what's called a "criminal"...and "criminals" are "arrested" because they aren't following laws. Now, some laws are lax because they are trivial, like jaywalking. However, laws that require people to not destroy property, not harm other people, etc. are considered some of the most critical laws, thus "arresting" "criminals" is necessary to ensure social civility.

I hate to go into Law 101 but liberals always seem to need the education; I even have to put important terms in quotes to make it easier to understand. The First Amendment specifically states "peacefully" so if you are not protesting "peacefully", then you are breaking the law making you a "criminal" and thus an "arrest" is warranted. Now, just like above, liberals are hard at work trying to get rid of "peacefully" from the First Amendment and, when they are successful, then these "arrests" will be against the law, thus making the government "criminals". But, until then, everyone is expected to follow the law. And, just to add in a little more elementary knowledge that liberals seem to ignore or just don't know, because you have a different opinion than the law does not mean you can break the law. Because of our wonderful governing documents, you have the ability to influence law changes so, if you go through the proper processes, you can help mold the law to your opinion. Until then, consider following the law or you will rightfully be "arrested".

"Yeah, pretty much all "arrests" facilitated by marines will immediately be thrown out"

The military gets involved to defuse the situation, not to make arrests, so your point isn't really relevant here.. They hand them over to the local authorities unless the protestors attack the military personnel, which is then a Federal crime and thus the military CAN arrest them.