There are a few responses to this but we need a little more context. Presumably this is not for a peer reviewed publication [I only ask this because you use the term 'major revisions']. At the end of the day your advisor is just that, your advisor, and it's up to you to decide how to, or if you should, implement the proposed changes. You don't have to implement all of them, you can defend your paper on those you feel strongly about, but remember that your advisor has a lot more experience than you and it's worth taking into account what they say, and that they may cause you to 'think outside the box' and revise your argument in ways you hadn't originally considered.
6 months sounds like an awfully long time to me between revisions. If you don't agree then say so, but justify your position. But remember that 'major revisions' are exactly that - major - and there must be a good reason why your advisor thinks that your paper[s] need changing to such a degree. I would sit down and talk things through, or if you're doing things over email, state which parts are most important to you and which you do/don't want to change and why.
Don't be too precious about your work. It's a learning experience and good research is generally the work of more than one person. I'm sure your advisor wants the best for you, and the field, so if you detach yourself from your product a little, you may have a better perspective.
