With all of the benefits that journaling can have, there can also be negative impacts if given too much priority in one's life. Like everything, journaling must be done in moderation, and should be used responsibly.
If you spend your time journaling by just going through the bad and the negatives in life, while blaming yourself and others in the process, you could just be reinforcing that negativity. This is especially true if these things are your main focus while journaling.
Remember, journaling is a tool to help you understand yourself better, and the world around you. If you focus only on the negatives in this world, it will be very difficult to find any positives. The more you linger on the negative parts of life, the harder it will be to let go of them and to focus on more positive aspects of life.