Do you think the constitution is a deeply flawed document written by the oligarchs of their time, which included among the institutions it codified slavery, misogyny, and war as a normal part of the human condition? Excellent, you're in good company and I (among many others) agree with you. That's why amendments and judges exist, also, so that we're not limited to its fairly flawed implementations and goals in governing what we're doing today.
Do you like having human rights, including the freedom to criticize the government, the right to due process, and the right to defend yourself against a tyrannical government? Great! So do I. As it happens there's a common phrasing that you can use as a quick code-word for saying that, which will engage the support of a massive range of people including among them conservatives, liberals, leftists, military people, police, lawyers, judges, and so on. And you know? It won't even made them want slavery back, if you do choose to say it that way. You could, of course, decide that it's more important to alienate 99% of those people immediately, and then provide fodder for extensive arguments with the remaining 1%. You could do that, that would be fun too.
Do you like having big performative "I'm more left than you so I'm superior I'm actually very smart because everything YOU think is good is actually bad" contests which assail whatever people are trying to do and distract from the most urgent issues of the day? Well... you're in good company with that one, too. This has always been a part of the left from the beginning, and I guess not for nothing; it's connected up with the freedom to speak your mind, not having to agree with any particular herd, and with having passion about issues and wanting to analyze everything and be on the right side of history. I get it. But I think the fight this person is picking is a pretty silly fight to pick right now.
100% of people you will talk to will understand what's meant by "the constitution," and literally nothing about it is anything other than urgent self-defense against a genuinely very urgent threat.