While that is definitely the case for me with my partner, I feel like it's not fair to say that a safeword is ALWAYS going to reduce the pleasure and thrill. Some people will find playing without a safeword to feel unsafe and will struggle to enjoy the experience, because they don't feel secure in what could happen. I don't like using safewords, and yet if I was playing with someone other than my partner, I would insist on one. NOT having it would reduce my pleasure and thrill. Talk to your lees (and lers). Let them tell you what they need and what will make the experience most enjoyable for them.
My statements on this apply only to my own personal preference. I'm not against safe words in general. I just don't want one myself.