Is eating too much sweet things good or bad for teeth?

Could be bad! Dental diseases such as "dental decay" and "periodontal" infections are caused by bacteria. These bacteria eat the sugar you consume in your diet. The metabolic waste from the bacteria eating the sugar is an acid. This acid can dissolve the enamel or irritate the "gums". If the bacteria are allowed to stay on the teeth they will cause decay or "gum" disease. Brushing/ floss removes the bacteria.
Yes. Doing anything "too much" is probably not the best. It's also important to brush your teeth & have a dental hygiene visit every 6 months.