Re: If you disagree with your instructor's explanations...
I guess you're stuck in a pretty bad situation right now.
But as you know, with the thousands if not millions of aikido practitioners in the world, you have to realize that what you perceive as basics is probably different from what your instructor might consider basics.
Take for example, an ex-commando that teaches aikido has a totally different mindset and skill sets when you compare it to a ki aikido instructor. what might be considered a tangible skill for instructor X might be considered hogwash by instructor Z. Compare that with the varying styles of aikido within aikikai itself. Most shihans are different if not VERY different from each other. some are very soft , and some are pretty hard. for example a aikidoka that studied under nishio sensei could/would put more emphasis on atemi, while someone else might focus exclusively on pure technique.
And you have to understand that aikido is for many people, many different things. For some, a way of life for others a way of self improvement. Some see it as a sport, some see it as self defense some just see it as a simple pass time. (cause movies and beer is getting more expensive nowadays :P)
But for your situation, if you are REALLY bugged by it, talk to the sensei privately. NO one wants to be countered in the middle of class especially when they're the sensei. It's always nice to offer the hand of diplomacy rather than shoot off about this or that being wrong.
But as far as I've seen, your probably get like 3 different type of replies
A --> Instructor thinks it's OK! and he even wants to learn from you
B --> Instructor thinks that it's OK, but isn't completely OK with it.(i.e. like maybe his/her students cant take ukemi the way which is required for a certain technique that you are advocating)
C --> Instructor calls you to shut the hell up.
I pray for you that he is the A type.
Another thing you have to consider is his view on the subject, he might think entering differently as better because it's safer, rather than being more flowing or any other reasons.
In the end, everyone that's teaching has something to give. you might not consider it useful or right NOW, but if you stick with it, you might see something in the future. If you really dun want it? It's ok to leave.
To do aikido is to enjoy it, no point having tension while following ueshiba's way to make better people. I don't think making bitter, angry people is the main goal of aikido.
hope this helps!
cheers from Singapore!
p.s. my English isn't really fantastic so bear with me.