I will be a freshman majoring in Computer Science at the University of Illinois at Urbana-Champaign next fall, and I'm interested in their B.S.-M.S. 5-year program. I ultimately want to get a Ph.D. in Computer Science so I can teach at a university. On the webpage documenting the B.S.-M.S. program it says:
Students are strongly advised to seek faculty counsel about the 5-yr program to be sure they understand the pros and cons of pursuing a Masters degree via the 5-yr program. If their intention is to ultimately pursue a Ph.D., then it may be preferable to avoid the rapid pace of the 5-year program and instead invest time in research as an undergraduate. For admission to competitive Ph.D. programs, the expectation of publications and extensive research experience is higher for M.S. graduates. Therefore, as an alternative to the 5-year program, many top students may prefer to conduct research, possibly leading to a B.S. thesis, as a way to improve their admissions chances into top Ph.D. programs.
This paragraph left me confused, because the M.S. program requires a thesis to graduate. I was always under the impression that thesis ≈ research. Wouldn't it be better preparation to acquire experience in graduate coursework and produce a Master's thesis than to simply get a B.S. thesis? It seems to me that according to this paragraph, the only reason to get a B.S. thesis instead of an M.S. thesis is to increase admissions chances to Ph.D. programs, because more is expected of M.S. students.
So, my main question is, how is a thesis different than research experience? Why is it worse to obtain an M.S. thesis (through a 5-year program) rather than a B.S. thesis, given I will apply to Ph.D. programs?