diff --git a/stix2/sources/memory.py b/stix2/sources/memory.py
index 9eca969..95d053c 100644
--- a/stix2/sources/memory.py
+++ b/stix2/sources/memory.py
@@ -22,33 +22,22 @@ import collections
 import json
 import os
 
-from stix2validator import validate_instance
-
 from stix2 import Bundle
 from stix2.sources import DataSink, DataSource, DataStore
 from stix2.sources.filters import Filter
 
 
-def _add(store, stix_data):
+def _add(store, stix_data=None):
     """Adds stix objects to MemoryStore/Source/Sink."""
     if isinstance(stix_data, collections.Mapping):
         # stix objects are in a bundle
-        # verify STIX json data
-        r = validate_instance(stix_data)
         # make dictionary of the objects for easy lookup
-        if r.is_valid:
-            for stix_obj in stix_data["objects"]:
-                store.data[stix_obj["id"]] = stix_obj
-        else:
-            raise ValueError("Error: data passed was found to not be valid by the STIX 2 Validator: \n%s", r.as_dict())
+        for stix_obj in stix_data["objects"]:
+            store.data[stix_obj["id"]] = stix_obj
     elif isinstance(stix_data, list):
         # stix objects are in a list
         for stix_obj in stix_data:
-            r = validate_instance(stix_obj)
-            if r.is_valid:
-                store.data[stix_obj["id"]] = stix_obj
-            else:
-                raise ValueError("Error: STIX object %s is not valid under STIX 2 validator.\n%s", stix_obj["id"], r)
+            store.data[stix_obj["id"]] = stix_obj
     else:
         raise ValueError("stix_data must be in bundle format or raw list")
 
@@ -56,7 +45,7 @@ def _add(store, stix_data):
 class MemoryStore(DataStore):
     """
     """
-    def __init__(self, stix_data):
+    def __init__(self, stix_data=None):
         """
         Notes:
             It doesn't make sense to create a MemoryStore by passing
@@ -83,7 +72,7 @@ class MemoryStore(DataStore):
 class MemorySink(DataSink):
     """
     """
-    def __init__(self, stix_data, _store=False):
+    def __init__(self, stix_data=None, _store=False):
         """
         Args:
             stix_data (dictionary OR list): valid STIX 2.0 content in
@@ -114,7 +103,7 @@ class MemorySink(DataSink):
 
 class MemorySource(DataSource):
 
-    def __init__(self, stix_data, _store=False):
+    def __init__(self, stix_data=None, _store=False):
         """
         Args:
             stix_data (dictionary OR list): valid STIX 2.0 content in
@@ -193,10 +182,5 @@ class MemorySource(DataSource):
         file_path = os.path.abspath(file_path)
         stix_data = json.load(open(file_path, "r"))
 
-        r = validate_instance(stix_data)
-
-        if r.is_valid:
-            for stix_obj in stix_data["objects"]:
-                    self.data[stix_obj["id"]] = stix_obj
-
-        raise ValueError("Error: STIX data loaded from file (%s) was found to not be validated by STIX 2 Validator.\n%s", file_path, r)
+        for stix_obj in stix_data["objects"]:
+            self.data[stix_obj["id"]] = stix_obj