Everyone is obligated per halacha to give tochacha when necessary.
The requirements to give Tochachah are:
1) You have to first assess that there is at least a reasonable possibility of the person listening to you. (Sometimes there are Halachic ways of assessing this.)
2) You have to give the Tochachah in a non-aggressive manner, and never in front of people.
3) You have to make the person understand that the only reason you are giving him the Tochachah is because you care about him, and it is for his good, so that he can get Olam Habah.
It also says in Sefer HaChinuch perek 239 that you should give someone tochacha privately and in a nice way; but if they don’t listen to you, then you should embarrass them in public so that they will do teshuvah.
As far as your other points: Nobody is questioning the fact that there are people who would be willing to be MO or not religious at all. The issue is, What is MO and is it the preferable mode of Judaism? The fact that it is, to some, the only version, or the maximum, that they are willing to accept does not address the issue at hand. If Modern Orthodoxy would be a Kiruv stage for people who aren’t yet ready for real Torah life, that would be fine. The problem is that they consider themselves not a b’dieved, but a l’chatchilah – a full fledged legitimate lifestyle. They often even make claims of being superior to Torah Judaism. That is the problem – compromises sometimes have to be made for individuals who are on their way up. But to take those compromises and make believe they are not compromises at all, thereby fooling people who WOULD be able to go higher that they need not, or worse, that they are already the highest, is a terrible crime. While it is true that on an individual, private, level, we are allowed to even proactively cause someone to sin if by doing so we will have prevented him form committing a greater sin, nevertheless, we may never, ever institutionalize those sins, making a b’dieved into a l’chatchilah, making the exception into the rule.
The reason why it would be a mistake to view MO as merely responding to the times as opposed to making compromises, is because when a response involves lowering standards it becomes, by definition, a compromise. MO has incorporated their inadequacies into Orthodoxy – they officially allow, encourage, and even support things that are wrong. They changed the definition of wrong and right. The difference between traditional Orthodoxy and MO in regard to meeting the times is NOT a difference of quantity. It is the difference between keeping exceptional cases as exceptions versus making them into the rule.
The problem with Modern Orthodoxy is not what their Jews do, but what their Judaism says. Jews are imperfect – we know that and accept it – but Judaism is perfect, and unchangeable. We do not make over G-d in our own image.