Man, there is some bad advice in here.

There are two inter-related but yet separate questions here.

1) what do you want your portfolio to be?

2) How do you best manage your CGT?

You probably should sell every single stock that is underwater for CGT purposes, as to maximise your harvested capital losses for tax purposes. Now, you can still turn around and re-buy these shares the day after, if you really still want them in your folio.

I would let question 2 be the main driver.

Generally, I would rather have a $100k of a "sub-optimal" folio then $90k of a "perfect" folio. Given that your sell choices do affect your CGT, and therefore your tax bill, this probably is the sort of choice that you face.