I'm not sure it's possible to ban criticism without also banning opinions. If you give a presentation on how some new tool or technique is good, you're implicitly implying that the existing alternatives aren't as good. Many presentations will even explicitly call out weaknesses in existing things (criticising them!) in order to illustrate why some new thing is worthwhile. If you talk about how your research fills in gaps left by some previous person's research, or how your software is suitable for use cases that someone else's isn't, then you're criticising the completeness of their efforts. But those are good, useful things to have in your talk. Making it clear to people what you're interested in, and why they might be interested in it too, is important, and I don't think that's possible to do without at least implicitly criticising other people's work.