It has been my experience time and again that the vast majority of people lip only what they hear and judge not for themselves, or know not for themselves. What is "bad" acting on Shatner's part? What is good acting on Shatner's part? Do they understand the context of a given era or period and have they seen Shatner play an array of roles?
Is Shatner the same character role after role, like Will Smith so often seems to be?
Is he wooden and stiff, devoid of energy, or can he breath life into a role; add color and dimension?
I grant that Shatner can be very animated, not just in his actions, but with his facial gestures and voice inflection, but I believe the vast majority doesn't know or has taken the time to do any research beyond their programming. Shatner is great at projecting character and energy; life into a character. He's an entertainer.
There are parrots all around us, and they grasp not why Shats was paid the big bucks, why he has endured over decades and to a great extent, why TOS was the enduring success that it has been.
Good and bad acting is much like human sexuality and attraction, very subjective.