So - the premise of what Dershowitz is saying here is fine. Sedition laws shouldn't be weaponized and used for politicization or to stifle legitimate protest.
The problem is his conclusion that it is being weaponized in this situation, is based on two false premises.
First, he says that "he thinks" that this was just a protest that "got out of hand." Okay, maybe that is accurate as far as a large segment of the protesters, but it doesn't address the specific facts of these 2 Oath Keepers. And, bottom line is, here the facts support way more than a mere protest that "got out of hand." There were texts/messages, testimony, etc. that supported that this was a premeditated act with the intent of harming people or worse and taking over Congress (what their long term plan was here assuming they succeeding in stopping the count, I have no idea). In any event, the only ones who are in a position to weigh these facts and determine whether it was a a "mere protest that got out of hand" or something more sinister was the jury -- not Dershowitz. And they made their decision based on the facts presented.
Second, Dershowitz compares this to some of the BLM riots around George Floyd and the Antifa protests. He has a point there too. The government needs to be super careful in seeking to enforce these laws against one side, but not the other - because it's a dangerous precedent to set. It's weaponizing the justice system for political gain, and once one side does it, it's a slippery slope. That's all fine, and correct - but we are really dealing with an unprecedented event here. You can make certain comparisons between the BLM/Antifa riots and 1/6, but the bottom line is the BLM/Antifa protests/riots did not deal with a premediated attack on the Capitol during the electoral vote count with the intent to take over Congress (you can disagree with that interpretation of the facts, but that's essentially what the jury found with regard to these two individuals at least). And, I'm not trying to diminish BLM/Antifa riots. They were terrible, and I fully believe the wrongdoers should be held fully accountable. But 1/6 generally (and these two Oath Keepers' acts specifically) is really on another level, and unprecedented. And, if you can't charge these Oath Keepers with sedition, then arguably, no conduct would rise to that level - and why even have the laws.
Lastly, everything Dershowitz says here should be taken with a grain of salt, since he is representing one of the protesters. Clearly, he can't speak in favor of the sedition laws or how they were used here - as it would likely harm his own client.