Against advice, when my infant son gets small bumps I often jump up to hold and comfort him while he bursts into tears. Is it true that I shouldn't react with this behaviour?

Personally I feel yes, you shouldn't make a big hoo ha. Kids are very independent by nature. They will know what to do if they fall. By showing them that you are so protective against them, they will be reliable on you and personally I feel that they will not learn. Let them learn the hard way now and they will know when to pick themselves up in future.