Cancel culture is also distinct from politicians and infidelity because cancel culture targets non-public individuals. Of course politicians and celebrities were always subject to public opinion; the modern era now means that everyone can be targeted this way, even if they weren't known at all before (Justine Sacco is a simple example).
The McCarthy era was again a matter of government action through government processes with at least some level of transparency, democratic representation, and accountability. It was not spontaneous mobs of individuals without leaders or any kind of accountability. (They also targeted communists, not just 'leftists').
It's ironic you say casually that "people today are getting canceled for exhibiting intolerance and bigotry", when cancel culture is itself intolerance and bigotry. The standard definition of bigotry is "extreme intolerance of any creed, belief, or opinion that differs from one's own." [0]
[0] https://www.thefreedictionary.com/bigotry
It's also always disturbing to encounter people like you who are openly clear that cancel culture is just like historical persecution, but you're totally fine with it because you (wrongly) think it only happens to bad people. As though only people you like deserve to have human rights.