“Well first of all, there’s direct radar evidence that US...

Macgregor, a special advisor to the secretary of defense under then-President Donald Trump, pointed out that explosives equivalent to thousands of pounds of TNT had to have been used to breach the pipelines. “You have several inches of concrete around various metal alloys to move the natural gas, so it’s not something that you could simply drop a grenade down at the end of a fish line and disrupt.”
Firstly, I would doubt the credibility of anyone connected with Trump.

Secondly, I don't think anyone doubts that this was the work of military forces, but anyone who thinks it would require thousands of pounds of TNT to rupture the Nord Stream pipelines, clearly has no idea of the power of explosives and in particular of shaped charges. Although, to be fair, it is not clear from the above exert that Macgregor actually said any such thing - it could merely be an inference made by the author of the article.

Below is a picture of the pipe used for Nord Stream (diameter is 1.22m)



“I think we’re on the very slippery, dangerous path that we never wanted to be on, which is the path to the end of NATO.”
If it is shown that the US or any other NATO country is responsible for the sabotage, he is probably right. Clearly other members, particularly Germany, would have to reconsider their position. This is the simplest and strongest reason to disbelieve these wild conspiracy theories.

“Well first of all, there’s direct radar evidence that US helicopters, military helicopters that are normally based in Gdansk, were circling over this area."

This is not evidence of an attack on the pipeline. How would helicopters circling the area be of any help in a covert sub-sea operation? Instead, this is possible evidence that the US were tracking the movements of a Russian submarine.

The US & NATO have hydrophones throughout the worlds oceans. These are most concentrated near Russian naval bases such as in the Baltic sea. The hydrophone network as augmented by satellite and aerial surveillance. If US helicopters were in fact circling the area at the time of the explosions, they were probably using magnetic anomaly detection to closely track a suspiciously behaving submarine that was already being tracked by the hydrophone network. If so, they will know which port the sub departed from, and from that information, coupled with it's noise signature, they will know exactly which sub (or subs) carried out the operation.

Don't listen to these conspiracy theories people. They will rot your brain. Many of them originate from Russia.