Q: My boss is constantly criticising the performance and work-style of senior members of the company and I am reluctant to add my agreement. (I don't agree anyway, and think he is just showing his own insecurity.) How do I avoid doing so without annoying him?
A: You seem to have avoided the biggest trap. If you'd as much as implied agreement, you'd have been sunk - forever complicit and never able to question his views.
Even so, it's terribly difficult. The only way that you can avoid the continuing need to dissemble is to get him to cut his criticisms - at least to you. And the only way you can achieve that is by putting it to him straight - or fairly straight, anyway.
Next time he starts to criticise his seniors, try saying something along these line: 'Look, Jake, I like my job and I like working with you, and I want to go on having faith in the company. So please don't tell me all this stuff about management: even if it's all true, there's nothing I can do about it and it's just going to rattle me. Hope you understand?'
You may have to say the same sort of thing a couple of times, but it should help. And with any luck, he won't take mortal offence.
In the longer term, he doesn't seem to me the sort of boss you want to go on working for.