They can't force you to accept the change ......

....... yet!   I have no doubt that in the next year or so you will HAVE to have a linked Google+ account in order to even use YouTube.   At the moment though it's just so bad that you can no longer comment without owning and linking to a Google+ account.  Here's a good video on the issue with a rant and explanation from another guy I subscribe to (HarshlyCritical):