Yea. That's one of the things I hear from people that switch from 4 to 5 or 6...muting. For those of us that play ERBs (Extended Range Bass: a bass that has 6 or more strings), knowing how to mute is must.
The 4-string-only people feel so strongly, because they look at guys like Victor Wooten, Marcus Miller, etc., then look at their local players who play 5/6 strings and say, he has more strings and he can't even do what Victor does, which is an unfair assessment of an ERB. If you take equally skilled player (both can tap, slap and play finger-style on an expert level), but one plays a 4-string and the other plays a 6-string, the 6-string will sound more "full" or complex, because of the extended range of the instrument. It doesn't mean that the person is "better" it's just that they can use the instrument to its fullest. How many of us, who have cars that can go 140mph, actually drive it that fast?...same thing. How many bass players only learn to play finger-style? How many bass players only play slap? How many bass players never learn to tap? The key to becoming a good musician, on any instrument, is to experiment with different ways of playing.