This is actually a very tricky scenario that you present. The real answer is yes, you can be sued. The reason for this is that it is very easy to sue nowadays. The real issue is the probability of you being sued. In this case, it may be very low depending on how public your statements become.
Another question to ask yourself is can you afford to be sued. This is a very costly proposition and can break you even if you are in the right.
Many good qualifying statements to use in a literature that you produce when it comes to speaking negatively about an entity include:
Based on my personal experience, if is my opinion that...
The opinion of this author is...
etc.
In this case you are relaying an opinion and any case filed against you is very weak. In the form of an oped type of writing, it is clearly stated that it is an opinion and as a general rule, opinions do not need to substantiated. They are opinions and nothing more and it is up to the reader to decide whether they agree with you.
I have found that it is best to let the reader draw their own conclusions and just present evidence, or specify that the piece is an opinion.