If true, it seems unlikely that marches and protests in recent days would be reaching record numbers. As it stands, the largest ever American march was the Women's March earlier this year. Other notable marches include the March for Science, the March for Women's Lives, the Armenian March for Justice, etc.
Sure, the internet allows armchair protestors the luxury of 'protesting' from home, but it's also a great tool for raising awareness, organizing, and it could be argued that even some amount of armchair protesting is beneficial, as it at least makes the cause visible to those who might not have seen it otherwise.
Let's face it, it would have been very hard to get the ~4 million protestors to march in DC without the internet.
"According to some experts, the initial excitement over the role of social media in political processes in the countries of the Maghreb and the Middle East has diminished. As Ekaterina Stepanova argues in her study concerning the role of information and communications technologies in the Arab Spring, social networks largely contributed to political and social mobilization but didn’t play a decisive and independent role in it. Instead, social media acted as a catalyst for revolution, as in the case of Egypt, where the existing gap between the ruling elite and the rest of the population would eventually have resulted in some kind of uprising."
That said, Malcolm Gladwell agrees with you -- that the low-risk protesting that social media provides is also basically without reward [1]
In the days of MLK if they had internet everyone would have just retweeted #marchonwashington.