Knee Doctor Diagnosis

So, for quite some time now, the inside of my left knee has been crackling and popping and for the most part acting somewhat "unstable".  Slight bending of the knee or applying pressure down to my feet causes my left knee to buckle very quickly.  It just seemed like I've lost support in my knees when I'm trying to exert a force from a bent knee position.

Visited a knee doctor specialist today and was told this was a common problem among runners and other sports involving impact to the knees.  The doctor asked me what sports I played and I answered "heavy weightlifting".  His tone from here on out got slightly aggressive and right off the bat he told me, "I'm biased against weightlifting".  Proceeded to tell me that squatting ass to grass is very bad for the knees and that I should instead be squatting only to 90 degrees.  In other words, doing partial squats (half, quarter), would alleviate the additional stresses on my knee joints.  Also, I have to avoid all impact-based training at all costs (no jumping, no walking, no running, etc.)  Instead, I should use the bike.

I get avoiding impact training for a while.  But, avoid below parallel squats?  I'll do parallel squats.  Maybe not ass to grass, but to avoid doing parallel squats completely isn't happening.